{"id":27090,"date":"2025-04-16T09:54:08","date_gmt":"2025-04-16T02:54:08","guid":{"rendered":"https:\/\/interdata.vn\/blog\/?p=27090"},"modified":"2025-05-03T17:15:33","modified_gmt":"2025-05-03T10:15:33","slug":"bien-la-gi","status":"publish","type":"post","link":"https:\/\/interdata.vn\/blog\/bien-la-gi\/","title":{"rendered":"Bi\u1ebfn l\u00e0 g\u00ec? C\u00e1c kh\u00e1i ni\u1ec7m, Vai tr\u00f2 &#038; C\u00e1c ki\u1ec3u d\u1eef li\u1ec7u c\u1ee7a bi\u1ebfn"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_85 counter-hierarchy ez-toc-counter ez-toc-white ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">N\u1ed8I DUNG<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" 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sao c\u1ea7n s\u1eed d\u1ee5ng bi\u1ebfn trong l\u1eadp tr\u00ecnh?<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Luu-tru-va-quan-ly-du-lieu-hieu-qua\" >L\u01b0u tr\u1eef v\u00e0 qu\u1ea3n l\u00fd d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Tang-kha-nang-doc-hieu-ma-nguon\" >T\u0103ng kh\u1ea3 n\u0103ng \u0111\u1ecdc hi\u1ec3u m\u00e3 ngu\u1ed3n<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Cho-phep-tai-su-dung-du-lieu\" >Cho ph\u00e9p t\u00e1i s\u1eed d\u1ee5ng d\u1eef li\u1ec7u<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#De-dang-thay-doi-va-bao-tri-ma-nguon\" >D\u1ec5 d\u00e0ng thay \u0111\u1ed5i v\u00e0 b\u1ea3o tr\u00ec m\u00e3 ngu\u1ed3n<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Cac-kieu-du-lieu-cua-bien\" >C\u00e1c ki\u1ec3u d\u1eef li\u1ec7u c\u1ee7a bi\u1ebfn<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Kieu-so-nguyen-Integer\" >Ki\u1ec3u s\u1ed1 nguy\u00ean (Integer)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Kieu-so-thuc-Floating-Point\" >Ki\u1ec3u s\u1ed1 th\u1ef1c (Floating-Point)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Kieu-chuoi-ky-tu-String\" >Ki\u1ec3u chu\u1ed7i k\u00fd t\u1ef1 (String)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Kieu-Logic-Boolean\" >Ki\u1ec3u Logic (Boolean)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Tai-sao-kieu-du-lieu-lai-quan-trong\" >T\u1ea1i sao ki\u1ec3u d\u1eef li\u1ec7u l\u1ea1i quan tr\u1ecdng?<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Mot-so-khai-niem-lien-quan-den-bien-nen-biet\" >M\u1ed9t s\u1ed1 kh\u00e1i ni\u1ec7m li\u00ean quan \u0111\u1ebfn bi\u1ebfn n\u00ean bi\u1ebft<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Khai-bao-bien-Variable-Declaration\" >Khai b\u00e1o bi\u1ebfn (Variable Declaration)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Gan-gia-tri-Value-Assignment\" >G\u00e1n gi\u00e1 tr\u1ecb (Value Assignment)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Khoi-tao-bien-Variable-Initialization\" >Kh\u1edfi t\u1ea1o bi\u1ebfn (Variable Initialization)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-17\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Ten-bien-va-Quy-tac-dat-ten-Variable-Name-Naming-Rules\" >T\u00ean bi\u1ebfn v\u00e0 Quy t\u1eafc \u0111\u1eb7t t\u00ean (Variable Name &amp; Naming Rules)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Hang-so-Constant\" >H\u1eb1ng s\u1ed1 (Constant)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/#Pham-vi-cua-bien-Variable-Scope\" >Ph\u1ea1m vi c\u1ee7a bi\u1ebfn (Variable Scope)<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n\n<p>T\u01b0\u1edfng t\u01b0\u1ee3ng bi\u1ebfn trong l\u1eadp tr\u00ecnh nh\u01b0 nh\u1eefng chi\u1ebfc h\u1ed9p \u0111a n\u0103ng c\u00f3 nh\u00e3n, gi\u00fap b\u1ea1n l\u01b0u tr\u1eef d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch ng\u0103n n\u1eafp v\u00e0 linh ho\u1ea1t. Hi\u1ec3u r\u00f5 bi\u1ebfn l\u00e0 g\u00ec ch\u00ednh l\u00e0 b\u01b0\u1edbc \u0111\u1ea7u ti\u00ean \u0111\u1ec3 vi\u1ebft code hi\u1ec7u qu\u1ea3. B\u00e0i vi\u1ebft n\u00e0y s\u1ebd \u0111\u1ecbnh ngh\u0129a bi\u1ebfn, n\u00eau b\u1eadt l\u1ee3i \u00edch (qu\u1ea3n l\u00fd d\u1eef li\u1ec7u, t\u00e1i s\u1eed d\u1ee5ng), kh\u00e1m ph\u00e1 c\u00e1c ki\u1ec3u d\u1eef li\u1ec7u th\u00f4ng d\u1ee5ng, v\u00e0 h\u01b0\u1edbng d\u1eabn b\u1ea1n c\u00e1c kh\u00e1i ni\u1ec7m then ch\u1ed1t nh\u01b0 khai b\u00e1o, g\u00e1n gi\u00e1 tr\u1ecb, ph\u00e2n bi\u1ec7t v\u1edbi h\u1eb1ng s\u1ed1 v\u00e0 hi\u1ec3u v\u1ec1 ph\u1ea1m vi.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Bien-la-gi\"><\/span>Bi\u1ebfn l\u00e0 g\u00ec?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><a href=\"https:\/\/interdata.vn\/blog\/bien-la-gi\/\">Bi\u1ebfn (Variable)<\/a> l\u00e0 m\u1ed9t t\u00ean g\u1ecdi \u0111\u1ea1i di\u1ec7n cho m\u1ed9t v\u1ecb tr\u00ed trong b\u1ed9 nh\u1edb m\u00e1y t\u00ednh, \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 l\u01b0u tr\u1eef d\u1eef li\u1ec7u. Hi\u1ec3u \u0111\u01a1n gi\u1ea3n, bi\u1ebfn gi\u1ed1ng nh\u01b0 m\u1ed9t chi\u1ebfc h\u1ed9p \u0111\u01b0\u1ee3c d\u00e1n nh\u00e3n t\u00ean, n\u01a1i b\u1ea1n c\u00f3 th\u1ec3 t\u1ea1m th\u1eddi c\u1ea5t gi\u1eef m\u1ed9t th\u00f4ng tin (g\u1ecdi l\u00e0 gi\u00e1 tr\u1ecb &#8211; Value) v\u00e0o \u0111\u00f3.<\/p>\n<p>Vi\u1ec7c s\u1eed d\u1ee5ng bi\u1ebfn gi\u00fap l\u1eadp tr\u00ecnh vi\u00ean qu\u1ea3n l\u00fd d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3 h\u01a1n khi vi\u1ebft m\u00e3 ngu\u1ed3n (Source Code). Thay v\u00ec l\u00e0m vi\u1ec7c tr\u1ef1c ti\u1ebfp v\u1edbi c\u00e1c \u0111\u1ecba ch\u1ec9 \u00f4 nh\u1edb ph\u1ee9c t\u1ea1p, ch\u00fang ta ch\u1ec9 c\u1ea7n d\u00f9ng t\u00ean bi\u1ebfn (v\u00ed d\u1ee5: <code>tuoi<\/code>, <code>hoTen<\/code>, <code>diemTrungBinh<\/code>) \u0111\u1ec3 truy c\u1eadp ho\u1eb7c thay \u0111\u1ed5i gi\u00e1 tr\u1ecb m\u00e0 n\u00f3 \u0111ang n\u1eafm gi\u1eef.<\/p>\n<p>H\u00e3y h\u00ecnh dung b\u1ea1n c\u00f3 m\u1ed9t h\u1ed9p ch\u1ee9a \u0111\u01b0\u1ee3c \u0111\u1eb7t t\u00ean l\u00e0 <code>soLuongSach<\/code> (\u0111\u00e2y l\u00e0 t\u00ean bi\u1ebfn). B\u00ean trong h\u1ed9p \u0111\u00f3, b\u1ea1n \u0111\u1eb7t con s\u1ed1 15 (\u0111\u00e2y l\u00e0 gi\u00e1 tr\u1ecb). Khi c\u1ea7n bi\u1ebft s\u1ed1 s\u00e1ch, b\u1ea1n ch\u1ec9 vi\u1ec7c t\u00ecm \u0111\u1ebfn h\u1ed9p <code>soLuongSach<\/code>. Gi\u00e1 tr\u1ecb 15 n\u00e0y c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt sau \u0111\u00f3, v\u00ed d\u1ee5 th\u00e0nh 20.<\/p>\n<p>M\u1ed7i bi\u1ebfn th\u01b0\u1eddng li\u00ean k\u1ebft v\u1edbi m\u1ed9t ki\u1ec3u d\u1eef li\u1ec7u (Data Type) c\u1ee5 th\u1ec3. Ki\u1ec3u d\u1eef li\u1ec7u quy \u0111\u1ecbnh lo\u1ea1i gi\u00e1 tr\u1ecb m\u00e0 bi\u1ebfn \u0111\u00f3 c\u00f3 th\u1ec3 l\u01b0u tr\u1eef (v\u00ed d\u1ee5: s\u1ed1 nguy\u00ean, ch\u1eef c\u00e1i, s\u1ed1 th\u1eadp ph\u00e2n) v\u00e0 c\u00e1ch m\u00e1y t\u00ednh x\u1eed l\u00fd d\u1eef li\u1ec7u \u0111\u00f3. \u0110i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u00fang c\u00e1ch.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/interdata.vn\/blog\/wp-content\/uploads\/2025\/04\/Bien-la-gi.jpg\" alt=\"Bi\u1ebfn l\u00e0 g\u00ec\" width=\"750\" height=\"500\" class=\"aligncenter size-full wp-image-27092\" title=\"\" srcset=\"https:\/\/interdata.vn\/blog\/wp-content\/uploads\/2025\/04\/Bien-la-gi.jpg 750w, https:\/\/interdata.vn\/blog\/wp-content\/uploads\/2025\/04\/Bien-la-gi-300x200.jpg 300w\" sizes=\"auto, (max-width: 750px) 100vw, 750px\" \/><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Tai-sao-can-su-dung-bien-trong-lap-trinh\"><\/span>T\u1ea1i sao c\u1ea7n s\u1eed d\u1ee5ng bi\u1ebfn trong l\u1eadp tr\u00ecnh?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>S\u1eed d\u1ee5ng bi\u1ebfn (variable) trong l\u1eadp tr\u00ecnh l\u00e0 c\u1ef1c k\u1ef3 c\u1ea7n thi\u1ebft v\u00ec ch\u00fang gi\u00fap l\u01b0u tr\u1eef d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch linh ho\u1ea1t, l\u00e0m cho m\u00e3 ngu\u1ed3n (source code) d\u1ec5 \u0111\u1ecdc, d\u1ec5 hi\u1ec3u h\u01a1n. \u0110\u1ed3ng th\u1eddi, bi\u1ebfn cho ph\u00e9p t\u00e1i s\u1eed d\u1ee5ng gi\u00e1 tr\u1ecb v\u00e0 d\u1ec5 d\u00e0ng c\u1eadp nh\u1eadt th\u00f4ng tin khi c\u1ea7n thi\u1ebft m\u00e0 kh\u00f4ng t\u1ed1n nhi\u1ec1u c\u00f4ng s\u1ee9c.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Luu-tru-va-quan-ly-du-lieu-hieu-qua\"><\/span>L\u01b0u tr\u1eef v\u00e0 qu\u1ea3n l\u00fd d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Bi\u1ebfn cung c\u1ea5p m\u1ed9t c\u00e1ch \u0111\u1eb7t t\u00ean d\u1ec5 nh\u1edb cho c\u00e1c gi\u00e1 tr\u1ecb quan tr\u1ecdng trong ch\u01b0\u01a1ng tr\u00ecnh c\u1ee7a b\u1ea1n. Thay v\u00ec ghi tr\u1ef1c ti\u1ebfp c\u00e1c con s\u1ed1 ho\u1eb7c chu\u1ed7i k\u00fd t\u1ef1 (g\u1ecdi l\u00e0 &#8220;hard-coding&#8221;), b\u1ea1n l\u01b0u tr\u1eef ch\u00fang v\u00e0o bi\u1ebfn. \u0110i\u1ec1u n\u00e0y gi\u00fap vi\u1ec7c qu\u1ea3n l\u00fd th\u00f4ng tin trong m\u00e3 ngu\u1ed3n tr\u1edf n\u00ean ng\u0103n n\u1eafp v\u00e0 c\u00f3 h\u1ec7 th\u1ed1ng h\u01a1n.<\/p>\n<p>V\u00ed d\u1ee5, thay v\u00ec vi\u1ebft <code>tinhDienTich = 3.14 * 5 * 5<\/code> nhi\u1ec1u l\u1ea7n trong ch\u01b0\u01a1ng tr\u00ecnh, b\u1ea1n c\u00f3 th\u1ec3 t\u1ea1o bi\u1ebfn <code>soPi = 3.14<\/code> v\u00e0 <code>banKinh = 5<\/code>. Sau \u0111\u00f3, b\u1ea1n ch\u1ec9 c\u1ea7n vi\u1ebft <code>tinhDienTich = soPi * banKinh * banKinh<\/code>. C\u00e1ch n\u00e0y gi\u00fap qu\u1ea3n l\u00fd c\u00e1c gi\u00e1 tr\u1ecb r\u00f5 r\u00e0ng v\u00e0 d\u1ec5 d\u00e0ng h\u01a1n.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Tang-kha-nang-doc-hieu-ma-nguon\"><\/span>T\u0103ng kh\u1ea3 n\u0103ng \u0111\u1ecdc hi\u1ec3u m\u00e3 ngu\u1ed3n<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>S\u1eed d\u1ee5ng t\u00ean bi\u1ebfn c\u00f3 \u00fd ngh\u0129a (v\u00ed d\u1ee5: <code>tongDiem<\/code>, <code>soLuongSanPham<\/code>, <code>tenKhachHang<\/code>) gi\u00fap m\u00e3 ngu\u1ed3n c\u1ee7a b\u1ea1n tr\u1edf n\u00ean d\u1ec5 \u0111\u1ecdc v\u00e0 d\u1ec5 hi\u1ec3u h\u01a1n r\u1ea5t nhi\u1ec1u. Ng\u01b0\u1eddi kh\u00e1c (v\u00e0 c\u1ea3 ch\u00ednh b\u1ea1n trong t\u01b0\u01a1ng lai) c\u00f3 th\u1ec3 nhanh ch\u00f3ng n\u1eafm b\u1eaft m\u1ee5c \u0111\u00edch c\u1ee7a d\u1eef li\u1ec7u \u0111ang \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng, thay v\u00ec ph\u1ea3i \u0111o\u00e1n \u00fd ngh\u0129a c\u1ee7a nh\u1eefng con s\u1ed1 v\u00f4 c\u1ea3m.<\/p>\n<p>H\u00e3y so s\u00e1nh hai c\u00e1ch vi\u1ebft: <code>ketQua = giaTriBanDau * 0.1<\/code> v\u00e0 <code>thueVAT = giaGoc * tiLeThueVAT<\/code>. R\u00f5 r\u00e0ng, c\u00e1ch th\u1ee9 hai s\u1eed d\u1ee5ng c\u00e1c t\u00ean bi\u1ebfn <code>thueVAT<\/code>, <code>giaGoc<\/code>, <code>tiLeThueVAT<\/code> gi\u00fap ng\u01b0\u1eddi \u0111\u1ecdc hi\u1ec3u ngay l\u1eadp t\u1ee9c ph\u00e9p t\u00ednh n\u00e0y \u0111ang l\u00e0m g\u00ec, l\u00e0m cho m\u00e3 ngu\u1ed3n s\u00e1ng s\u1ee7a v\u00e0 d\u1ec5 ti\u1ebfp c\u1eadn h\u01a1n.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Cho-phep-tai-su-dung-du-lieu\"><\/span>Cho ph\u00e9p t\u00e1i s\u1eed d\u1ee5ng d\u1eef li\u1ec7u<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Khi m\u1ed9t gi\u00e1 tr\u1ecb c\u1ea7n \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u1edf nhi\u1ec1u n\u01a1i kh\u00e1c nhau trong m\u00e3 ngu\u1ed3n, bi\u1ebfn l\u00e0 c\u00f4ng c\u1ee5 l\u00fd t\u01b0\u1edfng. B\u1ea1n ch\u1ec9 c\u1ea7n khai b\u00e1o bi\u1ebfn v\u00e0 g\u00e1n gi\u00e1 tr\u1ecb cho n\u00f3 m\u1ed9t l\u1ea7n duy nh\u1ea5t. Sau \u0111\u00f3, b\u1ea1n c\u00f3 th\u1ec3 g\u1ecdi t\u00ean bi\u1ebfn \u0111\u00f3 ra \u0111\u1ec3 d\u00f9ng l\u1ea1i \u1edf b\u1ea5t c\u1ee9 \u0111\u00e2u c\u1ea7n thi\u1ebft, tr\u00e1nh vi\u1ec7c l\u1eb7p l\u1ea1i d\u1eef li\u1ec7u.<\/p>\n<p>V\u00ed d\u1ee5, t\u00ean \u0111\u0103ng nh\u1eadp c\u1ee7a ng\u01b0\u1eddi d\u00f9ng c\u00f3 th\u1ec3 c\u1ea7n hi\u1ec3n th\u1ecb \u1edf nhi\u1ec1u m\u00e0n h\u00ecnh. B\u1ea1n ch\u1ec9 c\u1ea7n l\u01b0u t\u00ean v\u00e0o bi\u1ebfn <code>tenDangNhap<\/code> m\u1ed9t l\u1ea7n. Sau \u0111\u00f3, m\u1ecdi n\u01a1i c\u1ea7n hi\u1ec3n th\u1ecb ch\u1ec9 vi\u1ec7c g\u1ecdi bi\u1ebfn n\u00e0y. \u0110i\u1ec1u n\u00e0y kh\u00f4ng ch\u1ec9 ti\u1ebft ki\u1ec7m c\u00f4ng s\u1ee9c g\u00f5 l\u1ea1i m\u00e0 c\u00f2n \u0111\u1ea3m b\u1ea3o t\u00ednh nh\u1ea5t qu\u00e1n c\u1ee7a d\u1eef li\u1ec7u.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"De-dang-thay-doi-va-bao-tri-ma-nguon\"><\/span>D\u1ec5 d\u00e0ng thay \u0111\u1ed5i v\u00e0 b\u1ea3o tr\u00ec m\u00e3 ngu\u1ed3n<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>N\u1ebfu m\u1ed9t gi\u00e1 tr\u1ecb \u0111\u01b0\u1ee3c d\u00f9ng nhi\u1ec1u l\u1ea7n c\u1ea7n ph\u1ea3i thay \u0111\u1ed5i (v\u00ed d\u1ee5: l\u00e3i su\u1ea5t ng\u00e2n h\u00e0ng, t\u1ec9 l\u1ec7 thu\u1ebf), bi\u1ebfn l\u00e0m cho vi\u1ec7c c\u1eadp nh\u1eadt tr\u1edf n\u00ean \u0111\u01a1n gi\u1ea3n. B\u1ea1n ch\u1ec9 c\u1ea7n thay \u0111\u1ed5i gi\u00e1 tr\u1ecb t\u1ea1i n\u01a1i khai b\u00e1o bi\u1ebfn g\u1ed1c, v\u00e0 m\u1ecdi n\u01a1i kh\u00e1c trong m\u00e3 ngu\u1ed3n s\u1eed d\u1ee5ng bi\u1ebfn \u0111\u00f3 s\u1ebd t\u1ef1 \u0111\u1ed9ng \u00e1p d\u1ee5ng gi\u00e1 tr\u1ecb m\u1edbi.<\/p>\n<p>Th\u1eed t\u01b0\u1edfng t\u01b0\u1ee3ng b\u1ea1n d\u00f9ng tr\u1ef1c ti\u1ebfp s\u1ed1 <code>0.1<\/code> (10% thu\u1ebf) \u1edf 30 ch\u1ed7 trong code. Khi thu\u1ebf thay \u0111\u1ed5i th\u00e0nh <code>0.08<\/code> (8%), b\u1ea1n ph\u1ea3i t\u00ecm v\u00e0 s\u1eeda th\u1ee7 c\u00f4ng c\u1ea3 30 ch\u1ed7 \u0111\u00f3. Nh\u01b0ng n\u1ebfu b\u1ea1n d\u00f9ng bi\u1ebfn <code>tiLeThue = 0.1<\/code>, b\u1ea1n ch\u1ec9 c\u1ea7n s\u1eeda m\u1ed9t d\u00f2ng th\u00e0nh <code>tiLeThue = 0.08<\/code>, ti\u1ebft ki\u1ec7m th\u1eddi gian v\u00e0 gi\u1ea3m thi\u1ec3u r\u1ee7i ro ph\u00e1t sinh l\u1ed7i.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Cac-kieu-du-lieu-cua-bien\"><\/span>C\u00e1c ki\u1ec3u d\u1eef li\u1ec7u c\u1ee7a bi\u1ebfn<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Ki\u1ec3u d\u1eef li\u1ec7u (Data Type) trong l\u1eadp tr\u00ecnh quy \u0111\u1ecbnh lo\u1ea1i gi\u00e1 tr\u1ecb m\u00e0 m\u1ed9t bi\u1ebfn c\u00f3 th\u1ec3 l\u01b0u tr\u1eef v\u00e0 c\u00e1c ph\u00e9p to\u00e1n (nh\u01b0 c\u1ed9ng, tr\u1eeb, so s\u00e1nh) c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n tr\u00ean gi\u00e1 tr\u1ecb \u0111\u00f3. N\u00f3 gi\u00fap m\u00e1y t\u00ednh hi\u1ec3u v\u00e0 s\u1eed d\u1ee5ng d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong bi\u1ebfn m\u1ed9t c\u00e1ch ch\u00ednh x\u00e1c.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Kieu-so-nguyen-Integer\"><\/span>Ki\u1ec3u s\u1ed1 nguy\u00ean (Integer)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Ki\u1ec3u s\u1ed1 nguy\u00ean (Integer, th\u01b0\u1eddng vi\u1ebft t\u1eaft l\u00e0 int) \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 l\u01b0u tr\u1eef c\u00e1c s\u1ed1 nguy\u00ean, t\u1ee9c l\u00e0 nh\u1eefng s\u1ed1 kh\u00f4ng c\u00f3 ph\u1ea7n th\u1eadp ph\u00e2n. C\u00e1c s\u1ed1 n\u00e0y bao g\u1ed3m s\u1ed1 d\u01b0\u01a1ng, s\u1ed1 \u00e2m v\u00e0 s\u1ed1 kh\u00f4ng (0). \u0110\u00e2y l\u00e0 m\u1ed9t trong nh\u1eefng ki\u1ec3u d\u1eef li\u1ec7u c\u01a1 b\u1ea3n v\u00e0 th\u01b0\u1eddng g\u1eb7p nh\u1ea5t trong l\u1eadp tr\u00ecnh.<\/p>\n<p>V\u00ed d\u1ee5, b\u1ea1n c\u00f3 th\u1ec3 d\u00f9ng bi\u1ebfn ki\u1ec3u s\u1ed1 nguy\u00ean \u0111\u1ec3 l\u01b0u s\u1ed1 l\u01b0\u1ee3ng s\u1ea3n ph\u1ea9m: <code>soLuong = 50<\/code>, ho\u1eb7c l\u01b0u s\u1ed1 t\u1ea7ng trong t\u00f2a nh\u00e0: <code>soTang = -2<\/code> (n\u1ebfu c\u00f3 t\u1ea7ng h\u1ea7m), hay <code>soLoi = 0<\/code>. C\u00e1c bi\u1ebfn n\u00e0y kh\u00f4ng th\u1ec3 l\u01b0u gi\u00e1 tr\u1ecb nh\u01b0 <code>9.5<\/code> hay <code>\"Xin ch\u00e0o\"<\/code>.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Kieu-so-thuc-Floating-Point\"><\/span>Ki\u1ec3u s\u1ed1 th\u1ef1c (Floating-Point)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Ki\u1ec3u s\u1ed1 th\u1ef1c (Floating-point, th\u01b0\u1eddng g\u1ecdi l\u00e0 float ho\u1eb7c double) d\u00f9ng \u0111\u1ec3 bi\u1ec3u di\u1ec5n c\u00e1c s\u1ed1 c\u00f3 ph\u1ea7n th\u1eadp ph\u00e2n. Ki\u1ec3u d\u1eef li\u1ec7u n\u00e0y r\u1ea5t c\u1ea7n thi\u1ebft khi b\u1ea1n c\u1ea7n \u0111\u1ed9 ch\u00ednh x\u00e1c cao h\u01a1n s\u1ed1 nguy\u00ean, v\u00ed d\u1ee5 nh\u01b0 khi t\u00ednh to\u00e1n \u0111i\u1ec3m trung b\u00ecnh, gi\u00e1 ti\u1ec1n l\u1ebb, hay c\u00e1c th\u00f4ng s\u1ed1 khoa h\u1ecdc.<\/p>\n<p>V\u00ed d\u1ee5 v\u1ec1 gi\u00e1 tr\u1ecb ki\u1ec3u s\u1ed1 th\u1ef1c: <code>diemTrungBinh = 8.75<\/code>, <code>giaTien = 199.99<\/code>, <code>tyLeLaiSuat = 0.05<\/code>. Nh\u1eefng bi\u1ebfn n\u00e0y cho ph\u00e9p l\u01b0u tr\u1eef c\u00e1c con s\u1ed1 c\u00f3 ph\u1ea7n l\u1ebb, gi\u00fap th\u1ef1c hi\u1ec7n c\u00e1c ph\u00e9p t\u00ednh \u0111\u00f2i h\u1ecfi s\u1ef1 ch\u00ednh x\u00e1c v\u1ec1 m\u1eb7t th\u1eadp ph\u00e2n.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Kieu-chuoi-ky-tu-String\"><\/span>Ki\u1ec3u chu\u1ed7i k\u00fd t\u1ef1 (String)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Ki\u1ec3u chu\u1ed7i k\u00fd t\u1ef1 (String, th\u01b0\u1eddng vi\u1ebft t\u1eaft l\u00e0 str) \u0111\u01b0\u1ee3c d\u00f9ng \u0111\u1ec3 l\u01b0u tr\u1eef m\u1ed9t d\u00e3y c\u00e1c k\u00fd t\u1ef1, c\u00f3 th\u1ec3 l\u00e0 ch\u1eef c\u00e1i, ch\u1eef s\u1ed1, kho\u1ea3ng tr\u1eafng, hay c\u00e1c k\u00fd hi\u1ec7u \u0111\u1eb7c bi\u1ec7t. Gi\u00e1 tr\u1ecb c\u1ee7a m\u1ed9t bi\u1ebfn ki\u1ec3u chu\u1ed7i th\u01b0\u1eddng \u0111\u01b0\u1ee3c \u0111\u1eb7t b\u00ean trong c\u1eb7p d\u1ea5u nh\u00e1y \u0111\u01a1n (&#8216; &#8216;) ho\u1eb7c nh\u00e1y k\u00e9p (&#8221; &#8220;).<\/p>\n<p>V\u00ed d\u1ee5: <code>hoVaTen = \"L\u00ea Th\u1ecb B\u00ecnh\"<\/code>, <code>tenSach = 'L\u1eadp tr\u00ecnh C++'<\/code>, <code>thongBao = \"\u0110\u0103ng nh\u1eadp th\u00e0nh c\u00f4ng!\"<\/code>. Bi\u1ebfn ki\u1ec3u chu\u1ed7i c\u1ef1c k\u1ef3 h\u1eefu \u00edch \u0111\u1ec3 l\u00e0m vi\u1ec7c v\u1edbi d\u1eef li\u1ec7u d\u1ea1ng v\u0103n b\u1ea3n nh\u01b0 t\u00ean ng\u01b0\u1eddi, \u0111\u1ecba ch\u1ec9, m\u1eadt kh\u1ea9u, hay b\u1ea5t k\u1ef3 th\u00f4ng tin n\u00e0o c\u1ea7n hi\u1ec3n th\u1ecb d\u01b0\u1edbi d\u1ea1ng ch\u1eef.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Kieu-Logic-Boolean\"><\/span>Ki\u1ec3u Logic (Boolean)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Ki\u1ec3u logic (Boolean, th\u01b0\u1eddng vi\u1ebft t\u1eaft l\u00e0 bool) l\u00e0 m\u1ed9t ki\u1ec3u d\u1eef li\u1ec7u r\u1ea5t \u0111\u1eb7c bi\u1ec7t, n\u00f3 ch\u1ec9 c\u00f3 th\u1ec3 nh\u1eadn m\u1ed9t trong hai gi\u00e1 tr\u1ecb duy nh\u1ea5t: <code>True<\/code> (c\u00f3 ngh\u0129a l\u00e0 \u0110\u00fang) ho\u1eb7c <code>False<\/code> (c\u00f3 ngh\u0129a l\u00e0 Sai). Ki\u1ec3u d\u1eef li\u1ec7u n\u00e0y l\u00e0 n\u1ec1n t\u1ea3ng cho vi\u1ec7c ra quy\u1ebft \u0111\u1ecbnh trong l\u1eadp tr\u00ecnh.<\/p>\n<p>V\u00ed d\u1ee5: <code>daKichHoat = True<\/code>, <code>kiemTraLoi = False<\/code>. Ho\u1eb7c k\u1ebft qu\u1ea3 c\u1ee7a m\u1ed9t ph\u00e9p so s\u00e1nh c\u0169ng th\u01b0\u1eddng l\u00e0 Boolean: <code>duTuoiBauCu = (soTuoi &gt;= 18)<\/code>. Bi\u1ebfn Boolean gi\u00fap ch\u01b0\u01a1ng tr\u00ecnh ki\u1ec3m tra \u0111i\u1ec1u ki\u1ec7n v\u00e0 r\u1ebd nh\u00e1nh th\u1ef1c hi\u1ec7n c\u00e1c l\u1ec7nh kh\u00e1c nhau t\u01b0\u01a1ng \u1ee9ng.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Tai-sao-kieu-du-lieu-lai-quan-trong\"><\/span>T\u1ea1i sao ki\u1ec3u d\u1eef li\u1ec7u l\u1ea1i quan tr\u1ecdng?<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Vi\u1ec7c x\u00e1c \u0111\u1ecbnh \u0111\u00fang ki\u1ec3u d\u1eef li\u1ec7u cho bi\u1ebfn l\u00e0 v\u00f4 c\u00f9ng quan tr\u1ecdng trong l\u1eadp tr\u00ecnh. N\u00f3 gi\u00fap m\u00e1y t\u00ednh ph\u00e2n b\u1ed5 b\u1ed9 nh\u1edb (memory) m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3 \u0111\u1ec3 l\u01b0u tr\u1eef gi\u00e1 tr\u1ecb. \u0110\u1ed3ng th\u1eddi, n\u00f3 \u0111\u1ea3m b\u1ea3o c\u00e1c ph\u00e9p to\u00e1n \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n ch\u00ednh x\u00e1c v\u00e0 gi\u00fap ng\u0103n ng\u1eeba c\u00e1c l\u1ed7i kh\u00f4ng mong mu\u1ed1n ph\u00e1t sinh.<\/p>\n<p>Hi\u1ec3u r\u00f5 c\u00e1c ki\u1ec3u d\u1eef li\u1ec7u c\u01a1 b\u1ea3n s\u1ebd gi\u00fap b\u1ea1n s\u1eed d\u1ee5ng bi\u1ebfn m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3 h\u01a1n. \u0110i\u1ec1u n\u00e0y d\u1eabn \u0111\u1ebfn vi\u1ec7c vi\u1ebft m\u00e3 ngu\u1ed3n r\u00f5 r\u00e0ng, d\u1ec5 b\u1ea3o tr\u00ec v\u00e0 \u00edt l\u1ed7i h\u01a1n, b\u1ea5t k\u1ec3 b\u1ea1n \u0111ang h\u1ecdc hay l\u00e0m vi\u1ec7c v\u1edbi ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh (programming language) n\u00e0o \u0111i n\u1eefa.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Mot-so-khai-niem-lien-quan-den-bien-nen-biet\"><\/span>M\u1ed9t s\u1ed1 kh\u00e1i ni\u1ec7m li\u00ean quan \u0111\u1ebfn bi\u1ebfn n\u00ean bi\u1ebft<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>B\u00ean c\u1ea1nh \u0111\u1ecbnh ngh\u0129a bi\u1ebfn l\u00e0 g\u00ec, \u0111\u1ec3 l\u00e0m vi\u1ec7c hi\u1ec7u qu\u1ea3 v\u1edbi bi\u1ebfn trong l\u1eadp tr\u00ecnh, b\u1ea1n c\u1ea7n l\u00e0m quen th\u00eam m\u1ed9t s\u1ed1 kh\u00e1i ni\u1ec7m quan tr\u1ecdng kh\u00e1c. Ch\u00fang bao g\u1ed3m c\u00e1ch &#8220;t\u1ea1o ra&#8221; bi\u1ebfn (g\u1ecdi l\u00e0 khai b\u00e1o bi\u1ebfn), c\u00e1ch \u0111\u01b0a gi\u00e1 tr\u1ecb v\u00e0o bi\u1ebfn (g\u1ecdi l\u00e0 g\u00e1n gi\u00e1 tr\u1ecb), v\u00e0 c\u00e1c quy t\u1eafc c\u1ea7n bi\u1ebft.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Khai-bao-bien-Variable-Declaration\"><\/span>Khai b\u00e1o bi\u1ebfn (Variable Declaration)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Khai b\u00e1o bi\u1ebfn (Variable Declaration) l\u00e0 h\u00e0nh \u0111\u1ed9ng \u0111\u1ea7u ti\u00ean \u0111\u1ec3 gi\u1edbi thi\u1ec7u m\u1ed9t t\u00ean bi\u1ebfn m\u1edbi v\u1edbi ch\u01b0\u01a1ng tr\u00ecnh l\u1eadp tr\u00ecnh. Qua \u0111\u00f3, b\u1ea1n th\u00f4ng b\u00e1o cho ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh bi\u1ebft r\u1eb1ng b\u1ea1n d\u1ef1 \u0111\u1ecbnh s\u1eed d\u1ee5ng m\u1ed9t bi\u1ebfn v\u1edbi t\u00ean c\u1ee5 th\u1ec3 \u0111\u00f3 \u0111\u1ec3 l\u01b0u tr\u1eef d\u1eef li\u1ec7u. M\u1ed9t s\u1ed1 ng\u00f4n ng\u1eef y\u00eau c\u1ea7u ch\u1ec9 \u0111\u1ecbnh c\u1ea3 ki\u1ec3u d\u1eef li\u1ec7u khi khai b\u00e1o.<\/p>\n<p>V\u00ed d\u1ee5, trong ng\u00f4n ng\u1eef C++ ho\u1eb7c Java, b\u1ea1n c\u00f3 th\u1ec3 khai b\u00e1o bi\u1ebfn <code>tuoi<\/code> ki\u1ec3u s\u1ed1 nguy\u00ean b\u1eb1ng c\u00e2u l\u1ec7nh: <code>int tuoi;<\/code>. Trong JavaScript ho\u1eb7c Python, vi\u1ec7c n\u00e0y c\u00f3 th\u1ec3 \u0111\u01a1n gi\u1ea3n h\u01a1n, \u0111\u00f4i khi ch\u1ec9 c\u1ea7n g\u00e1n gi\u00e1 tr\u1ecb l\u00e0 \u0111\u1ee7 \u0111\u1ec3 khai b\u00e1o. M\u1ee5c \u0111\u00edch l\u00e0 \u0111\u1ec3 ch\u01b0\u01a1ng tr\u00ecnh &#8220;bi\u1ebft&#8221; v\u1ec1 s\u1ef1 t\u1ed3n t\u1ea1i c\u1ee7a bi\u1ebfn.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Gan-gia-tri-Value-Assignment\"><\/span>G\u00e1n gi\u00e1 tr\u1ecb (Value Assignment)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>G\u00e1n gi\u00e1 tr\u1ecb (Assignment) l\u00e0 thao t\u00e1c \u0111\u01b0a m\u1ed9t gi\u00e1 tr\u1ecb c\u1ee5 th\u1ec3 v\u00e0o m\u1ed9t bi\u1ebfn \u0111\u00e3 \u0111\u01b0\u1ee3c khai b\u00e1o tr\u01b0\u1edbc \u0111\u00f3. Trong h\u1ea7u h\u1ebft c\u00e1c ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh, ph\u00e9p g\u00e1n \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n b\u1eb1ng d\u1ea5u b\u1eb1ng (<code>=<\/code>). Gi\u00e1 tr\u1ecb n\u1eb1m \u1edf b\u00ean ph\u1ea3i d\u1ea5u <code>=<\/code> s\u1ebd \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef v\u00e0o bi\u1ebfn c\u00f3 t\u00ean \u1edf b\u00ean tr\u00e1i.<\/p>\n<p>Ti\u1ebfp n\u1ed1i v\u00ed d\u1ee5 tr\u00ean, sau khi khai b\u00e1o <code>int tuoi;<\/code>, b\u1ea1n c\u00f3 th\u1ec3 g\u00e1n gi\u00e1 tr\u1ecb 25 cho bi\u1ebfn n\u00e0y: <code>tuoi = 25;<\/code>. K\u1ec3 t\u1eeb l\u00fac n\u00e0y, bi\u1ebfn <code>tuoi<\/code> s\u1ebd ch\u1ee9a gi\u00e1 tr\u1ecb 25. V\u00ec l\u00e0 bi\u1ebfn, b\u1ea1n ho\u00e0n to\u00e0n c\u00f3 th\u1ec3 g\u00e1n m\u1ed9t gi\u00e1 tr\u1ecb kh\u00e1c cho n\u00f3 sau n\u00e0y, v\u00ed d\u1ee5: <code>tuoi = 26;<\/code>.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Khoi-tao-bien-Variable-Initialization\"><\/span>Kh\u1edfi t\u1ea1o bi\u1ebfn (Variable Initialization)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Kh\u1edfi t\u1ea1o bi\u1ebfn (Initialization) l\u00e0 vi\u1ec7c k\u1ebft h\u1ee3p c\u1ea3 hai b\u01b0\u1edbc: khai b\u00e1o bi\u1ebfn v\u00e0 g\u00e1n gi\u00e1 tr\u1ecb ban \u0111\u1ea7u cho n\u00f3, ch\u1ec9 trong m\u1ed9t c\u00e2u l\u1ec7nh duy nh\u1ea5t. Vi\u1ec7c n\u00e0y gi\u00fap m\u00e3 ngu\u1ed3n c\u1ee7a b\u1ea1n ng\u1eafn g\u1ecdn h\u01a1n v\u00e0 quan tr\u1ecdng l\u00e0 \u0111\u1ea3m b\u1ea3o bi\u1ebfn lu\u00f4n c\u00f3 m\u1ed9t gi\u00e1 tr\u1ecb x\u00e1c \u0111\u1ecbnh ngay khi n\u00f3 \u0111\u01b0\u1ee3c t\u1ea1o ra.<\/p>\n<p>Thay v\u00ec vi\u1ebft hai d\u00f2ng <code>int diemThi;<\/code> v\u00e0 <code>diemThi = 9;<\/code>, b\u1ea1n c\u00f3 th\u1ec3 kh\u1edfi t\u1ea1o bi\u1ebfn <code>diemThi<\/code> ngay l\u1eadp t\u1ee9c: <code>int diemThi = 9;<\/code>. Trong Python, b\u1ea1n ch\u1ec9 c\u1ea7n vi\u1ebft: <code>diemThi = 9<\/code>. C\u00e2u l\u1ec7nh n\u00e0y v\u1eeba khai b\u00e1o bi\u1ebfn <code>diemThi<\/code>, v\u1eeba g\u00e1n gi\u00e1 tr\u1ecb ban \u0111\u1ea7u l\u00e0 9 cho n\u00f3.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Ten-bien-va-Quy-tac-dat-ten-Variable-Name-Naming-Rules\"><\/span>T\u00ean bi\u1ebfn v\u00e0 Quy t\u1eafc \u0111\u1eb7t t\u00ean (Variable Name &amp; Naming Rules)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>T\u00ean bi\u1ebfn (Variable Name), hay c\u00f2n g\u1ecdi l\u00e0 \u0111\u1ecbnh danh (identifier), l\u00e0 c\u00e1i t\u00ean b\u1ea1n s\u1eed d\u1ee5ng \u0111\u1ec3 g\u1ecdi v\u00e0 thao t\u00e1c v\u1edbi bi\u1ebfn. Vi\u1ec7c ch\u1ecdn t\u00ean bi\u1ebfn r\u00f5 r\u00e0ng, mang t\u00ednh g\u1ee3i nh\u1edb (v\u00ed d\u1ee5: <code>soLuongDonHang<\/code>, <code>tenNguoiDung<\/code>) l\u00e0 c\u1ef1c k\u1ef3 quan tr\u1ecdng, gi\u00fap m\u00e3 ngu\u1ed3n d\u1ec5 \u0111\u1ecdc, d\u1ec5 hi\u1ec3u v\u00e0 d\u1ec5 b\u1ea3o tr\u00ec h\u01a1n.<\/p>\n<p>H\u1ea7u h\u1ebft c\u00e1c ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh c\u00f3 quy t\u1eafc \u0111\u1eb7t t\u00ean bi\u1ebfn t\u01b0\u01a1ng t\u1ef1 nhau: th\u01b0\u1eddng b\u1eaft \u0111\u1ea7u b\u1eb1ng ch\u1eef c\u00e1i ho\u1eb7c d\u1ea5u g\u1ea1ch d\u01b0\u1edbi (<code>_<\/code>), kh\u00f4ng ch\u1ee9a kho\u1ea3ng tr\u1eafng, kh\u00f4ng d\u00f9ng k\u00fd t\u1ef1 \u0111\u1eb7c bi\u1ec7t (ngo\u1ea1i tr\u1eeb <code>_<\/code>). Nhi\u1ec1u ng\u00f4n ng\u1eef ph\u00e2n bi\u1ec7t ch\u1eef hoa v\u00e0 ch\u1eef th\u01b0\u1eddng (<code>tuoi<\/code> kh\u00e1c v\u1edbi <code>Tuoi<\/code>). B\u1ea1n c\u1ea7n tu\u00e2n th\u1ee7 quy \u01b0\u1edbc c\u1ee7a t\u1eebng ng\u00f4n ng\u1eef.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Hang-so-Constant\"><\/span>H\u1eb1ng s\u1ed1 (Constant)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>H\u1eb1ng s\u1ed1 (Constant) v\u1ec1 b\u1ea3n ch\u1ea5t c\u0169ng l\u00e0 m\u1ed9t t\u00ean g\u1ecdi d\u00f9ng \u0111\u1ec3 l\u01b0u tr\u1eef gi\u00e1 tr\u1ecb, gi\u1ed1ng nh\u01b0 bi\u1ebfn. Tuy nhi\u00ean, \u0111i\u1ec3m kh\u00e1c bi\u1ec7t m\u1ea5u ch\u1ed1t l\u00e0 gi\u00e1 tr\u1ecb c\u1ee7a h\u1eb1ng s\u1ed1 kh\u00f4ng th\u1ec3 b\u1ecb thay \u0111\u1ed5i sau khi \u0111\u00e3 \u0111\u01b0\u1ee3c g\u00e1n l\u1ea7n \u0111\u1ea7u ti\u00ean. N\u00f3 s\u1ebd gi\u1eef nguy\u00ean gi\u00e1 tr\u1ecb \u0111\u00f3 trong su\u1ed1t qu\u00e1 tr\u00ecnh ch\u01b0\u01a1ng tr\u00ecnh ch\u1ea1y.<\/p>\n<p>V\u00ed d\u1ee5, s\u1ed1 Pi (~3.14159) l\u00e0 m\u1ed9t gi\u00e1 tr\u1ecb kh\u00f4ng \u0111\u1ed5i, n\u00ean th\u01b0\u1eddng \u0111\u01b0\u1ee3c khai b\u00e1o l\u00e0 h\u1eb1ng s\u1ed1: <code>const double PI = 3.14159;<\/code>. Sau khi khai b\u00e1o, b\u1ea1n kh\u00f4ng th\u1ec3 th\u1ef1c hi\u1ec7n ph\u00e9p g\u00e1n m\u1edbi nh\u01b0 <code>PI = 3.14;<\/code>. H\u1eb1ng s\u1ed1 gi\u00fap \u0111\u1ea3m b\u1ea3o c\u00e1c gi\u00e1 tr\u1ecb quan tr\u1ecdng kh\u00f4ng b\u1ecb v\u00f4 t\u00ecnh thay \u0111\u1ed5i.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Pham-vi-cua-bien-Variable-Scope\"><\/span>Ph\u1ea1m vi c\u1ee7a bi\u1ebfn (Variable Scope)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Ph\u1ea1m vi c\u1ee7a bi\u1ebfn (Variable Scope) \u0111\u1ecbnh ngh\u0129a khu v\u1ef1c trong m\u00e3 ngu\u1ed3n m\u00e0 t\u1ea1i \u0111\u00f3 bi\u1ebfn c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c truy c\u1eadp v\u00e0 s\u1eed d\u1ee5ng h\u1ee3p l\u1ec7. M\u1ed9t bi\u1ebfn ch\u1ec9 &#8220;s\u1ed1ng&#8221; v\u00e0 c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c g\u1ecdi t\u00ean b\u00ean trong ph\u1ea1m vi \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh c\u1ee7a n\u00f3. \u0110i\u1ec1u n\u00e0y gi\u00fap tr\u00e1nh xung \u0111\u1ed9t t\u00ean bi\u1ebfn v\u00e0 qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb hi\u1ec7u qu\u1ea3.<\/p>\n<p>C\u00f3 hai lo\u1ea1i ph\u1ea1m vi ch\u00ednh: bi\u1ebfn c\u1ee5c b\u1ed9 (local variable) \u0111\u01b0\u1ee3c khai b\u00e1o b\u00ean trong m\u1ed9t h\u00e0m ho\u1eb7c kh\u1ed1i l\u1ec7nh v\u00e0 ch\u1ec9 d\u00f9ng \u0111\u01b0\u1ee3c trong \u0111\u00f3 v\u00e0 bi\u1ebfn to\u00e0n c\u1ee5c (global variable) \u0111\u01b0\u1ee3c khai b\u00e1o b\u00ean ngo\u00e0i m\u1ecdi h\u00e0m, c\u00f3 th\u1ec3 truy c\u1eadp t\u1eeb b\u1ea5t k\u1ef3 \u0111\u00e2u. Hi\u1ec3u v\u1ec1 ph\u1ea1m vi l\u00e0 r\u1ea5t quan tr\u1ecdng khi l\u1eadp tr\u00ecnh.<\/p>\n<div style=\"background-color: #e6f2ff; border-radius: 10px; padding: 20px; margin: 20px 0; border: 1px solid #b3d9ff;\">\n<p>Khi b\u1ea1n \u00e1p d\u1ee5ng c\u00e1c kh\u00e1i ni\u1ec7m nh\u01b0 bi\u1ebfn \u0111\u1ec3 x\u00e2y d\u1ef1ng website hay \u1ee9ng d\u1ee5ng \u0111\u1ea7u tay, b\u1ea1n s\u1ebd c\u1ea7n m\u1ed9t n\u1ec1n t\u1ea3ng \u0111\u00e1ng tin c\u1eady \u0111\u1ec3 \u0111\u01b0a s\u1ea3n ph\u1ea9m c\u1ee7a m\u00ecnh l\u00ean m\u1ea1ng. D\u1ecbch v\u1ee5 <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https:\/\/interdata.vn\/thue-hosting\/\">thu\u00ea Hosting<\/a> t\u1ea1i InterData cung c\u1ea5p m\u00f4i tr\u01b0\u1eddng \u1ed5n \u0111\u1ecbnh, t\u1ed1c \u0111\u1ed9 cao v\u1edbi dung l\u01b0\u1ee3ng \u0111\u01b0\u1ee3c t\u1ed1i \u01b0u tr\u00ean ph\u1ea7n c\u1ee9ng chuy\u00ean d\u1ee5ng th\u1ebf h\u1ec7 m\u1edbi, gi\u00fap d\u1ef1 \u00e1n c\u1ee7a b\u1ea1n kh\u1edfi \u0111\u1ea7u thu\u1eadn l\u1ee3i.<\/p>\n<p>V\u1edbi nh\u1eefng d\u1ef1 \u00e1n \u0111\u00f2i h\u1ecfi c\u1ea5u h\u00ecnh m\u1ea1nh m\u1ebd h\u01a1n, c\u1ea7n nhi\u1ec1u t\u00e0i nguy\u00ean v\u00e0 s\u1ef1 linh ho\u1ea1t, vi\u1ec7c <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https:\/\/interdata.vn\/thue-vps\/\">thu\u00ea VPS gi\u00e1 r\u1ebb<\/a> l\u00e0 m\u1ed9t gi\u1ea3i ph\u00e1p ch\u1ea5t l\u01b0\u1ee3ng v\u00e0 uy t\u00edn. Ngo\u00e0i ra, b\u1ea1n c\u00f3 th\u1ec3 kh\u00e1m ph\u00e1 d\u1ecbch v\u1ee5 <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https:\/\/interdata.vn\/cloud-server\/\">thu\u00ea Cloud Server gi\u00e1 r\u1ebb<\/a> s\u1eed d\u1ee5ng c\u00f4ng ngh\u1ec7 \u1ea3o h\u00f3a ti\u00ean ti\u1ebfn, b\u1ed9 x\u1eed l\u00fd AMD EPYC Gen 3th v\u00e0 SSD NVMe U.2 cho hi\u1ec7u n\u0103ng v\u01b0\u1ee3t tr\u1ed9i c\u00f9ng b\u0103ng th\u00f4ng cao.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>T\u01b0\u1edfng t\u01b0\u1ee3ng bi\u1ebfn trong l\u1eadp tr\u00ecnh nh\u01b0 nh\u1eefng chi\u1ebfc h\u1ed9p \u0111a n\u0103ng c\u00f3 nh\u00e3n, gi\u00fap b\u1ea1n l\u01b0u tr\u1eef d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch ng\u0103n n\u1eafp v\u00e0 linh ho\u1ea1t. Hi\u1ec3u r\u00f5 bi\u1ebfn l\u00e0 g\u00ec ch\u00ednh l\u00e0 b\u01b0\u1edbc \u0111\u1ea7u ti\u00ean \u0111\u1ec3 vi\u1ebft code hi\u1ec7u qu\u1ea3. B\u00e0i vi\u1ebft n\u00e0y s\u1ebd \u0111\u1ecbnh ngh\u0129a bi\u1ebfn, n\u00eau b\u1eadt l\u1ee3i \u00edch (qu\u1ea3n l\u00fd<\/p>\n","protected":false},"author":2,"featured_media":27092,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[140],"tags":[],"class_list":["post-27090","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-lap-trinh"],"_links":{"self":[{"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/posts\/27090","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/comments?post=27090"}],"version-history":[{"count":2,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/posts\/27090\/revisions"}],"predecessor-version":[{"id":27093,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/posts\/27090\/revisions\/27093"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/media\/27092"}],"wp:attachment":[{"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/media?parent=27090"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/categories?post=27090"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/interdata.vn\/blog\/wp-json\/wp\/v2\/tags?post=27090"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}