{"id":12407,"date":"2013-08-23T09:10:00","date_gmt":"2013-08-23T09:10:00","guid":{"rendered":"https:\/\/kiencang.net\/2013\/08\/23\/cach-viet-cau-lenh-if-trong-php\/"},"modified":"2013-08-23T09:10:00","modified_gmt":"2013-08-23T09:10:00","slug":"cach-viet-cau-lenh-if-trong-php","status":"publish","type":"post","link":"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/","title":{"rendered":"C\u00e1ch vi\u1ebft c\u00e2u l\u1ec7nh if trong PHP"},"content":{"rendered":"\n<p>L\u1ec7nh if trong PHP l\u00e0 l\u1ec7nh hay \u0111\u01b0\u1ee3c d\u00f9ng v\u00e0 r\u1ea5t quan tr\u1ecdng. N\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 \u0111i\u1ec1u khi\u1ec3n vi\u1ec7c th\u1ef1c thi c\u00e1c l\u1ec7nh d\u1ef1a tr\u00ean <a href=\"https:\/\/kiencang.net\/true-va-false-trong-php\/\" target=\"_blank\" rel=\"noreferrer noopener\">k\u1ebft qu\u1ea3 TRUE ho\u1eb7c FALSE<\/a> c\u1ee7a m\u1ed9t ho\u1eb7c nhi\u1ec1u bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n.<\/p>\n\n\n\n<p>V\u1ec1 c\u1ea5u tr\u00fac th\u00ec \u0111o\u1ea1n code d\u01b0\u1edbi \u0111\u00e2y tr\u00ecnh b\u00e0y c\u1ea5u tr\u00fac t\u1ed5ng qu\u00e1t v\u00e0 \u0111\u1ea7y \u0111\u1ee7 c\u1ee7a c\u00e2u l\u1ec7nh if:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if (Bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n 1) {\nKh\u1ed1i l\u1ec7nh \u0111\u01b0\u1ee3c th\u1ef1c thi 1\n}\nelse if (Bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n 2) {\nKh\u1ed1i l\u1ec7nh \u0111\u01b0\u1ee3c th\u1ef1c thi 2\n}\nelse if (Bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n n) {\nKh\u1ed1i l\u1ec7nh \u0111\u01b0\u1ee3c th\u1ef1c thi n\n}\nelse {\nKh\u1ed1i l\u1ec7nh \u0111\u01b0\u1ee3c th\u1ef1c thi cu\u1ed1i c\u00f9ng\n}<\/code><\/pre>\n\n\n\n<p>Bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n s\u1ebd \u0111\u01b0\u1ee3c \u0111\u01b0a v\u00e0o trong d\u1ea5u ngo\u1eb7c \u0111\u01a1n <code>()<\/code>, c\u00f2n kh\u1ed1i l\u1ec7nh th\u1ef1c thi \u0111\u01b0\u1ee3c \u0111\u01b0a v\u00e0o trong d\u1ea5u ngo\u1eb7c nh\u1ecdn <code>{}<\/code><\/p>\n\n\n\n<p>Ch\u1ec9 khi n\u00e0o <strong>bi\u1ec3u th\u1ee9c<\/strong> \u0111i\u1ec1u ki\u1ec7n c\u00f3 gi\u00e1 tr\u1ecb TRUE th\u00ec <strong>kh\u1ed1i l\u1ec7nh<\/strong> b\u00ean trong t\u01b0\u01a1ng \u1ee9ng m\u1edbi \u0111\u01b0\u1ee3c th\u1ef1c thi, c\u00f2n kh\u00f4ng th\u00ec ch\u01b0\u01a1ng tr\u00ecnh s\u1ebd b\u1ecf qua \u0111\u1ec3 \u0111i t\u1edbi xem x\u00e9t bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n ti\u1ebfp theo.<\/p>\n\n\n\n<p>N\u1ebfu bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n c\u00f3 gi\u00e1 tr\u1ecb TRUE th\u00ec kh\u1ed1i l\u1ec7nh b\u00ean trong t\u01b0\u01a1ng \u1ee9ng \u0111\u01b0\u1ee3c th\u1ef1c thi, c\u00e1c bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n v\u00e0 kh\u1ed1i l\u1ec7nh kh\u00e1c c\u1ee7a h\u00e0m if \u0111\u00f3 s\u1ebd b\u1ecb b\u1ecf qua.<\/p>\n\n\n\n<p>C\u00e2u l\u1ec7nh <strong>c\u00f3 th\u1ec3 ch\u1ee9a nhi\u1ec1u m\u1ec7nh \u0111\u1ec1 else if<\/strong> nh\u01b0ng ch\u1ec9 \u0111\u01b0\u1ee3c ph\u00e9p <strong>ch\u1ee9a duy nh\u1ea5t 1 m\u1ec7nh \u0111\u1ec1 else<\/strong> v\u00e0 n\u00f3 ph\u1ea3i \u1edf v\u1ecb tr\u00ed cu\u1ed1i c\u00f9ng (kh\u00f4ng t\u00ednh m\u1ec7nh \u0111\u1ec1 else kh\u00e1c trong c\u00e2u l\u1ec7nh if l\u1ed3ng)<\/p>\n\n\n\n<p>M\u1ec7nh \u0111\u1ec1 else cu\u1ed1i c\u00f9ng kh\u00f4ng c\u00f3 bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n \u0111i k\u00e8m m\u00e0 ch\u1ec9 c\u00f3 kh\u1ed1i l\u1ec7nh th\u1ef1c thi. Khi t\u1ea5t c\u1ea3 c\u00e1c \u0111i\u1ec1u ki\u1ec7n if v\u00e0 else if \u0111\u1ec1u sai th\u00ec l\u00fac \u0111\u00f3 kh\u1ed1i l\u1ec7nh th\u1ef1c thi c\u1ee7a else cu\u1ed1i c\u00f9ng m\u1edbi \u0111\u01b0\u1ee3c ch\u1ea1y&#8230;<\/p>\n\n\n\n<p>Trong th\u1ef1c t\u1ebf kh\u00f4ng ph\u1ea3i l\u00fac n\u00e0o b\u1ea1n c\u0169ng vi\u1ebft \u0111\u1ea7y \u0111\u1ee7 c\u1ea5u tr\u00fac tr\u00ean do v\u1eady c\u00f3 t\u1edbi 3 c\u00e1ch vi\u1ebft cho c\u00e2u l\u1ec7nh if, t\u00f9y theo m\u1ee5c \u0111\u00edch m\u00e0 n\u00ean s\u1eed d\u1ee5ng c\u00e1i n\u00e0o cho ph\u00f9 h\u1ee3p.<\/p>\n\n\n\n<hr class=\"wp-block-separator\"\/>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_60 counter-hierarchy ez-toc-counter ez-toc-light-blue ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title \" >M\u1ee5c l\u1ee5c<\/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\" role=\"button\"><label for=\"item-6577d68928110\" ><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\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input aria-label=\"Toggle\" aria-label=\"item-6577d68928110\"  type=\"checkbox\" id=\"item-6577d68928110\"><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/#Cau_lenh_if_khong_co_menh_de_nao_khac_di_kem\" title=\"C\u00e2u l\u1ec7nh if kh\u00f4ng c\u00f3 m\u1ec7nh \u0111\u1ec1 n\u00e0o kh\u00e1c \u0111i k\u00e8m\">C\u00e2u l\u1ec7nh if kh\u00f4ng c\u00f3 m\u1ec7nh \u0111\u1ec1 n\u00e0o kh\u00e1c \u0111i k\u00e8m<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/#Cau_lenh_if_co_menh_de_else_di_kem\" title=\"C\u00e2u l\u1ec7nh if c\u00f3 m\u1ec7nh \u0111\u1ec1 else \u0111i k\u00e8m\">C\u00e2u l\u1ec7nh if c\u00f3 m\u1ec7nh \u0111\u1ec1 else \u0111i k\u00e8m<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/#Cau_lenh_if_co_ca_menh_de_else_if_va_else\" title=\"C\u00e2u l\u1ec7nh if c\u00f3 c\u1ea3 m\u1ec7nh \u0111\u1ec1 else if v\u00e0 else\">C\u00e2u l\u1ec7nh if c\u00f3 c\u1ea3 m\u1ec7nh \u0111\u1ec1 else if v\u00e0 else<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/#Cau_lenh_if_voi_bieu_thuc_dieu_kien_phuc\" title=\"C\u00e2u l\u1ec7nh if v\u1edbi bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n ph\u1ee9c\">C\u00e2u l\u1ec7nh if v\u1edbi bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n ph\u1ee9c<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/#Nhung_loi_hay_xay_ra_voi_if\" title=\"Nh\u1eefng l\u1ed7i hay x\u1ea3y ra v\u1edbi if\">Nh\u1eefng l\u1ed7i hay x\u1ea3y ra v\u1edbi if<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Cau_lenh_if_khong_co_menh_de_nao_khac_di_kem\"><\/span>C\u00e2u l\u1ec7nh if kh\u00f4ng c\u00f3 m\u1ec7nh \u0111\u1ec1 n\u00e0o kh\u00e1c \u0111i k\u00e8m<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>if (bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n) {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n}<\/code><\/pre>\n\n\n\n<p><span style=\"font-family: inherit;\"><b>V\u00ed d\u1ee5:<\/b>&nbsp;<\/span><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if ($tuoi >= 18) {\necho '\u0110\u01b0\u1ee3c c\u1ea5p b\u1eb1ng l\u00e1i xe';\n}<\/code><\/pre>\n\n\n\n<p><span style=\"font-family: inherit;\"><b>Gi\u1ea3i th\u00edch: <\/b>N\u1ebfu bi\u1ebfn $tuoi c\u00f3 gi\u00e1 tr\u1ecb l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 18 th\u00ec in ra d\u00f2ng ch\u1eef \u0110\u01b0\u1ee3c c\u1ea5p b\u1eb1ng l\u00e1i xe.<\/span><\/p>\n\n\n\n<hr class=\"wp-block-separator\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Cau_lenh_if_co_menh_de_else_di_kem\"><\/span>C\u00e2u l\u1ec7nh if c\u00f3 m\u1ec7nh \u0111\u1ec1 else \u0111i k\u00e8m<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>if (bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n) {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n} else {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n}<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><b><span style=\"font-family: inherit;\">V\u00ed d\u1ee5:<\/span><\/b><\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>if ($tuoi >= 18) {\necho '\u0110\u01b0\u1ee3c c\u1ea5p b\u1eb1ng l\u00e1i xe';\n}\nelse {\necho 'Ch\u01b0a \u0111\u1ee7 tu\u1ed5i!'\n}<\/code><\/pre>\n\n\n\n<p><b>Gi\u1ea3i th\u00edch:\u00a0<\/b>N\u1ebfu bi\u1ebfn $tuoi c\u00f3 gi\u00e1 tr\u1ecb l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 18 th\u00ec in ra d\u00f2ng ch\u1eef &#8216;\u0110\u01b0\u1ee3c c\u1ea5p b\u1eb1ng l\u00e1i xe&#8217;. C\u00f2n n\u1ebfu kh\u00f4ng th\u00ec in ra d\u00f2ng ch\u1eef &#8216;Ch\u01b0a \u0111\u1ee7 tu\u1ed5i&#8217;.<\/p>\n\n\n\n<hr class=\"wp-block-separator\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Cau_lenh_if_co_ca_menh_de_else_if_va_else\"><\/span>C\u00e2u l\u1ec7nh if c\u00f3 c\u1ea3 m\u1ec7nh \u0111\u1ec1 else if v\u00e0 else<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>if (bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n) {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n} else if (bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n) {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n} else {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi\n}<\/code><\/pre>\n\n\n\n<p><b><span style=\"font-family: inherit;\">V\u00ed d\u1ee5:<\/span><\/b><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if ($diem_tong_ket >= 8) {\n$xep_loai = 'B\u1eb1ng gi\u1ecfi';\n}\nelse if ($diem_tong_ket >= 7) {\n$xep_loai = 'B\u1eb1ng kh\u00e1';\n}\nelse if ($diem_tong_ket >= 6) {\n$xep_loai = 'Trung b\u00ecnh kh\u00e1';\n}\nelse if ($diem_tong_ket >= 5) {\n$xep_loai = 'Trung b\u00ecnh';\n}\nelse {\necho 'H\u1ecdc l\u1ea1i!';\n}<\/code><\/pre>\n\n\n\n<p><b>Gi\u1ea3i th\u00edch:\u00a0<\/b><\/p>\n\n\n\n<ul><li>N\u1ebfu bi\u1ebfn\u00a0<span style=\"font-family: 'Courier New', Courier, monospace;\">$diem_tong_ket<\/span>\u00a0c\u00f3 gi\u00e1 tr\u1ecb l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 8 th\u00ec in ra d\u00f2ng ch\u1eef &#8216;B\u1eb1ng gi\u1ecfi&#8217;. <\/li><li>N\u1ebfu kh\u00f4ng l\u1edbn h\u01a1n 8 v\u00e0 \u0111\u1ed3ng th\u1eddi l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 7 th\u00ec in ra d\u00f2ng ch\u1eef &#8216;B\u1eb1ng kh\u00e1&#8217;. <\/li><li>N\u1ebfu kh\u00f4ng l\u1edbn h\u01a1n 7 v\u00e0 \u0111\u1ed3ng th\u1eddi l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 6 th\u00ec in ra d\u00f2ng ch\u1eef &#8216;Trung b\u00ecnh kh\u00e1&#8217;. <\/li><li>N\u1ebfu kh\u00f4ng l\u1edbn h\u01a1n 6 v\u00e0 \u0111\u1ed1ng th\u1eddi l\u1edbn h\u01a1n ho\u1eb7c b\u1eb1ng 5 th\u00ec in &#8216;Trung b\u00ecnh&#8217;. <\/li><li>Cu\u1ed1i c\u00f9ng, ngo\u00e0i t\u1ea5t c\u1ea3 c\u00e1c tr\u01b0\u1eddng h\u1ee3p tr\u00ean &#8211; t\u1ee9c l\u00e0 nh\u1ecf h\u01a1n 5 th\u00ec s\u1ebd in ra d\u00f2ng &#8216;H\u1ecdc l\u1ea1i!&#8217;<\/li><\/ul>\n\n\n\n<hr class=\"wp-block-separator\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Cau_lenh_if_voi_bieu_thuc_dieu_kien_phuc\"><\/span><span style=\"font-family: inherit;\">C\u00e2u l\u1ec7nh if v\u1edbi bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n ph\u1ee9c<\/span><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p><span style=\"font-family: inherit;\">S\u1ebd kh\u00f4ng ch\u1ec9 c\u00f3 1 bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n m\u00e0 s\u1ebd c\u00f3 v\u00e0i bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n c\u00f9ng k\u1ebft h\u1ee3p v\u1edbi nhau \u0111\u1ec3 xem x\u00e9t. N\u00f3 c\u0169ng gi\u1ed1ng nh\u01b0 ki\u1ec3u b\u1ea1n ch\u1ecdn mua m\u1ed9t c\u00e1i \u0111i\u1ec7n tho\u1ea1i, n\u00f3 s\u1ebd ph\u1ea3i th\u1ecfa m\u00e3n v\u00e0i \u0111i\u1ec1u ki\u1ec7n, ch\u1eb3ng h\u1ea1n kh\u00f4ng c\u00f3 gi\u00e1 qu\u00e1 7 tri\u1ec7u, ph\u1ea3i l\u00e0 \u0111i\u1ec7n tho\u1ea1i th\u00f4ng minh, c\u00f3 \u0111\u1ecbnh v\u1ecb to\u00e0n c\u1ea7u, h\u00e3ng s\u1ea3n xu\u1ea5t l\u00e0 Iphone ho\u1eb7c SamSung&#8230;B\u1ea1n c\u00f3 th\u1ec3 ch\u1ecdn b\u1eaft bu\u1ed9c ph\u1ea3i th\u1ecfa m\u00e3n c\u1ea3 4 \u0111i\u1ec1u ki\u1ec7n tr\u00ean th\u00ec m\u1edbi mua ho\u1eb7c c\u0169ng c\u00f3 th\u1ec3 ch\u1ecdn th\u1ecfa m\u00e3n \u00edt nh\u1ea5t 3\/4 th\u00ec b\u1ea1n c\u0169ng mua&#8230;<\/span><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if (bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n 1 to\u00e1n t\u1eed logic bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n 2 to\u00e1n t\u1eed logic bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n 3...) {\nkh\u1ed1i l\u1ec7nh th\u1ef1c thi;\n}<\/code><\/pre>\n\n\n\n<p><b><span style=\"font-family: inherit;\">V\u00ed d\u1ee5:<\/span><\/b><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if (empty($so_luong) || !is_numeric($so_luong) || ($so_luong &lt;=0)) {\n$thong_diep = 'S\u1ed1 l\u01b0\u1ee3ng ph\u1ea3i \u0111\u01b0\u1ee3c nh\u1eadp v\u00e0 ph\u1ea3i l\u00e0 m\u1ed9t s\u1ed1 nguy\u00ean d\u01b0\u01a1ng';\n}<\/code><\/pre>\n\n\n\n<p><span style=\"font-family: inherit;\"><b>Gi\u1ea3i th\u00edch: <\/b>D\u00f2ng code tr\u00ean ki\u1ec3m tra xem bi\u1ebfn $so_luong c\u00f3 \u0111\u01b0\u1ee3c nh\u1eadp hay kh\u00f4ng b\u1eb1ng h\u00e0m empty(), ti\u1ebfp \u0111\u1ebfn n\u00f3 ki\u1ec3m tra d\u1eef li\u1ec7u nh\u1eadp v\u00e0o c\u00f3 ph\u1ea3i l\u00e0 m\u1ed9t s\u1ed1 hay kh\u00f4ng b\u1eb1ng h\u00e0m is_numeric(), cu\u1ed1i c\u00f9ng l\u00e0 x\u00e1c th\u1ef1c s\u1ed1 nh\u1eadp v\u00e0o ph\u1ea3i c\u00f3 gi\u00e1 tr\u1ecb d\u01b0\u01a1ng. B\u1ea1n c\u00f3 th\u1ec3 k\u1ebft h\u1ee3p t<a href=\"https:\/\/kiencang.net\/toan-tu-so-sanh-va-toan-tu-logic-trong-php\/\" target=\"_blank\" rel=\"noreferrer noopener\">o\u00e1n t\u1eed so s\u00e1nh v\u1edbi to\u00e1n t\u1eed logic nh\u01b0 &amp;&amp;, ||, !<\/a> trong bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n ph\u1ee9c.<\/span><br><span style=\"font-family: Courier New, Courier, monospace;\"><br><\/span><span style=\"font-family: inherit;\">Ngo\u00e0i ra c\u00f2n c\u00f3 c\u00e2u l\u1ec7nh if l\u1ed3ng &#8211; t\u1ee9c l\u00e0 c\u00e2u l\u1ec7nh if n\u00e0y l\u1ed3ng trong c\u00e2u l\u1ec7nh if kh\u00e1c.<\/span><\/p>\n\n\n\n<hr class=\"wp-block-separator\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Nhung_loi_hay_xay_ra_voi_if\"><\/span>Nh\u1eefng l\u1ed7i hay x\u1ea3y ra v\u1edbi if<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>1. Nh\u1ea7m so s\u00e1nh b\u1eb1ng th\u00e0nh g\u00e1n, v\u00ed d\u1ee5 \u0111\u00e1ng ra mu\u1ed1n so s\u00e1nh bi\u1ebfn $a c\u00f3 b\u1eb1ng 5 hay kh\u00f4ng, ta ph\u1ea3i vi\u1ebft l\u00e0 <code>$a == 5<\/code>, th\u00ec ch\u00fang ta l\u1ea1i vi\u1ebft l\u00e0 <code>$a = 5<\/code><\/p>\n\n\n\n<p>2. \u0110\u1ec3 d\u1ea5u ch\u1ea5m ph\u1ea9y b\u00ean ngo\u00e0i ngo\u1eb7c nh\u1ecdn, v\u00ed d\u1ee5:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>$a = 6;\n$b = 5;\n$c = 7;\n\nif ($a > $b &amp;&amp; $c > 5) {echo \"c\u1ea3 hai \u0111i\u1ec1u ki\u1ec7n \u0111\u1ec1u \u0111\u00fang\"};<\/code><\/pre>\n\n\n\n<p>3. Bi\u1ebfn ch\u01b0a kh\u1edfi t\u1ea1o, v\u00ed d\u1ee5:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n$b = 5;\n$c = 7;\n\nif ($a > $b &amp;&amp; $c > 5) {echo \"c\u1ea3 hai \u0111i\u1ec1u ki\u1ec7n \u0111\u1ec1u \u0111\u00fang\"};\n\n\/\/ bi\u1ebfn $a ch\u01b0a \u0111\u01b0\u1ee3c kh\u1edfi t\u1ea1o<\/code><\/pre>\n\n\n\n<p>\u0110\u1ec3 kh\u1eafc ph\u1ee5c \u0111i\u1ec1u n\u00e0y, \u0111\u1ed1i v\u1edbi c\u00e1c bi\u1ebfn ch\u01b0a ch\u1eafc l\u00e0 \u0111\u00e3 kh\u1edfi t\u1ea1o hay ch\u01b0a, ta n\u00ean ki\u1ec3m tra tr\u01b0\u1edbc n\u00f3 b\u1eb1ng c\u00e2u l\u1ec7nh isset(), v\u00ed d\u1ee5:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>$b = 5;\n$c = 7;\n\nif (isset($a)) {\n    if ($a > $b &amp;&amp; $c > 5) {echo \"c\u1ea3 hai \u0111i\u1ec1u ki\u1ec7n \u0111\u1ec1u \u0111\u00fang\";}\n}<\/code><\/pre>\n\n\n\n<p>4. If l\u1ed3ng qu\u00e1 nhi\u1ec1u<\/p>\n\n\n\n<p>Th\u1ef1c ra \u0111\u00e2y kh\u00f4ng ph\u1ea3i l\u00e0 l\u1ed7i, nh\u01b0ng m\u1ed9t s\u1ed1 IDE nh\u01b0 Apache Neatbeans s\u1ebd \u0111\u01b0a ra c\u1ea3nh b\u00e1o n\u1ebfu n\u00f3 th\u1ea5y b\u1ea1n vi\u1ebft c\u00f3 nhi\u1ec1u if l\u1ed3ng v\u00e0o nhau, n\u1ebfu t\u00f4i nh\u1edb kh\u00f4ng nh\u1ea7m l\u00e0 t\u1eeb 3 \u0111\u1ed5 l\u00ean l\u00e0 s\u1ebd c\u1ea3nh b\u00e1o.<\/p>\n\n\n\n<p>L\u00fd do if l\u1ed3ng nhi\u1ec1u nguy hi\u1ec3m l\u00e0 n\u00f3 d\u1ec5 g\u00e2y ra nh\u1ea7m l\u1eabn k\u1ec3 c\u1ea3 v\u1ec1 m\u1eb7t d\u00f2ng l\u1ec7nh th\u1eeba thi\u1ebfu d\u1ea5u n\u1ecd d\u1ea5u kia, c\u0169ng nh\u01b0 logic c\u00f3 th\u1ec3 c\u00f3 v\u1ea5n \u0111\u1ec1, d\u1ec5 g\u00e2y l\u1eabn l\u1ed9n. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>L\u1ec7nh if trong PHP l\u00e0 l\u1ec7nh hay \u0111\u01b0\u1ee3c d\u00f9ng v\u00e0 r\u1ea5t quan tr\u1ecdng. N\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 \u0111i\u1ec1u khi\u1ec3n vi\u1ec7c th\u1ef1c thi c\u00e1c l\u1ec7nh d\u1ef1a tr\u00ean k\u1ebft qu\u1ea3 TRUE ho\u1eb7c FALSE c\u1ee7a m\u1ed9t ho\u1eb7c nhi\u1ec1u bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n. V\u1ec1 c\u1ea5u tr\u00fac th\u00ec \u0111o\u1ea1n code d\u01b0\u1edbi \u0111\u00e2y tr\u00ecnh b\u00e0y c\u1ea5u tr\u00fac t\u1ed5ng qu\u00e1t v\u00e0 &hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[238],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>C\u00e1ch vi\u1ebft c\u00e2u l\u1ec7nh if trong PHP &#8226; Ki\u1ebfn c\u00e0ng<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"C\u00e1ch vi\u1ebft c\u00e2u l\u1ec7nh if trong PHP &#8226; Ki\u1ebfn c\u00e0ng\" \/>\n<meta property=\"og:description\" content=\"L\u1ec7nh if trong PHP l\u00e0 l\u1ec7nh hay \u0111\u01b0\u1ee3c d\u00f9ng v\u00e0 r\u1ea5t quan tr\u1ecdng. N\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 \u0111i\u1ec1u khi\u1ec3n vi\u1ec7c th\u1ef1c thi c\u00e1c l\u1ec7nh d\u1ef1a tr\u00ean k\u1ebft qu\u1ea3 TRUE ho\u1eb7c FALSE c\u1ee7a m\u1ed9t ho\u1eb7c nhi\u1ec1u bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n. V\u1ec1 c\u1ea5u tr\u00fac th\u00ec \u0111o\u1ea1n code d\u01b0\u1edbi \u0111\u00e2y tr\u00ecnh b\u00e0y c\u1ea5u tr\u00fac t\u1ed5ng qu\u00e1t v\u00e0 &hellip;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/\" \/>\n<meta property=\"og:site_name\" content=\"Ki\u1ebfn c\u00e0ng\" \/>\n<meta property=\"article:author\" content=\"https:\/\/www.facebook.com\/anhducnguyen87\/\" \/>\n<meta property=\"article:published_time\" content=\"2013-08-23T09:10:00+00:00\" \/>\n<meta name=\"author\" content=\"Nguy\u1ec5n \u0110\u1ee9c Anh\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"\u0110\u01b0\u1ee3c vi\u1ebft b\u1edfi\" \/>\n\t<meta name=\"twitter:data1\" content=\"Nguy\u1ec5n \u0110\u1ee9c Anh\" \/>\n\t<meta name=\"twitter:label2\" content=\"\u01af\u1edbc t\u00ednh th\u1eddi gian \u0111\u1ecdc\" \/>\n\t<meta name=\"twitter:data2\" content=\"6 ph\u00fat\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"C\u00e1ch vi\u1ebft c\u00e2u l\u1ec7nh if trong PHP &#8226; Ki\u1ebfn c\u00e0ng","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/kiencang.net\/cach-viet-cau-lenh-if-trong-php\/","og_locale":"vi_VN","og_type":"article","og_title":"C\u00e1ch vi\u1ebft c\u00e2u l\u1ec7nh if trong PHP &#8226; Ki\u1ebfn c\u00e0ng","og_description":"L\u1ec7nh if trong PHP l\u00e0 l\u1ec7nh hay \u0111\u01b0\u1ee3c d\u00f9ng v\u00e0 r\u1ea5t quan tr\u1ecdng. N\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 \u0111i\u1ec1u khi\u1ec3n vi\u1ec7c th\u1ef1c thi c\u00e1c l\u1ec7nh d\u1ef1a tr\u00ean k\u1ebft qu\u1ea3 TRUE ho\u1eb7c FALSE c\u1ee7a m\u1ed9t ho\u1eb7c nhi\u1ec1u bi\u1ec3u th\u1ee9c \u0111i\u1ec1u ki\u1ec7n. 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