Number, floating point, Boolean, string, and array (php Tutorial 1)

For example:

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$ Fa = 3.14;

Strings and arrays are reference types. That is to say, they are placed in the stack as addresses. When a value is assigned again, the address in the stack changes direction. The original direction is lost or recycled: string and array.

For example: $ str = "string"; $ arr = array ("a" => "number", "B" => "group"); // array () it is an array assignment function. There are more than one thousand such functions in php, and less than 200 are commonly used, I think.

String operation:

Instance 2: string merging and addition
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<? Php $ Str = 1; Echo $ str. = ""; // The number is converted to a string and then merged. Result: "1 ". Echo "<br> "; Echo $ str + = "1 RMB"; // The string is converted to a number and then added. For example, if "1xxx" is converted to a number 1, the result is 2. Echo "<br> "; ?>

Instance 3: The string is case-insensitive.
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<? Php $ Str = "12345abc "; Echo strtolower ($ str); // The result is "12345abc ". Echo "<br> "; Echo strtoupper ($ str); // small write, result: "12345abc ". Echo "<br> "; ?>

Example 4: string length, substring truncation (Chinese and English)
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<? Php $ Str = "string 2 "; Echo mb_strlen ($ str, "UTF-8"); // return the string length function. The second parameter is Encoding. This is because the page is encoded with UTF-8. If this parameter is omitted, the number of bytes in memory (ascii) is returned, that is, 10. Result 4: Echo "<br> "; Echo mb_substr ($ str, 1, 2, "UTF-8"); // returns the truncation of characters. 1 is the truncation starting from the "character" address, 2 is a string of 2 UTF-8 encoded characters ". Echo "<br> "; /** * Knowledge Point: now you are new to functions. Each function has () as a stack call. () contains 0 or more parameters, which can be customized with default values. For example, echo does not have a keyword. * Many books are encoded in gb2312 format. It is difficult to get the length and substring. The following is a reference to the implementation principle of the above mb Chinese character string extension Library: */ Function my_mb_strlen ($ str, $ code = "UTF-8") // defines a new function. $ str is a required parameter. {$ Num = 0; If ($ code = "UTF-8 ") { $ Str = iconv ("UTF-8", "gb2312", $ str); // Convert to gb2312 encoding. The ord function returns the corresponding ascii value to determine whether the Chinese character of each byte ends. For ($ I = 0; $ I <strlen ($ str); $ I ++) // in this strlen ($ str) the number of bytes occupied by the returned memory is equivalent to mb_strlen ($ str) { If (ord ($ str [$ I])> 0xa0) $ I ++; // $ str [$ I] corresponds to the memory I bytes. If UTF-8 is used directly, it will be more complicated, because the diversity of encoding UTF-8 is commonly used for webpage encoding, and UTF-16 (unicode) is windows encoding. $ Num ++; } } Else { $ Num = "encoding not implemented "; } // Check your information if you are interested. Return $ num; } Echo my_mb_strlen ($ str ). ";". my_mb_strlen ($ str, "gb2312 "). "<br>"; // This page is encoded in UTF-8, but you can say that the input string 3 is gb2312, which cannot be correct even if the function is implemented. ?>

Instance 5: Search and replace substrings

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<? Php $ Str = "string 4 "; Echo mb_strpos ($ str, 'string4', 0, "UTF-8"); // you can specify the position of the first substring from 0. The result is 2. If no value is found, null (= "") is returned. If the last two parameters are not found, 6 is returned. Echo "<br> "; Echo mb_strstr ($ str, 'string', 0, "UTF-8"); // extract the first substring found from 0 to the end. The result is "string 4 ". If no value is found, null (= "") is returned. If the last two parameters are not found, the same = strstr ($ str, 'string') is returned '). Echo "<br> "; Echo str_replace ("4", "not 4", $ str); // string replacement. Result: "The string is not 4 ". Echo "<br> "; ?>

Example 6: empty and html escape of the substring
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<? Php $ Str = "string 5 "; Echo $ str = trim ($ str); // remove spaces on both sides. Result: "string 5 ". Echo "<br> "; Echo "color =" red ""; // manually convert the preceding ', "to store it in the memory. The result is" color = "red "" Echo "<br> "; $ Str = "<br> 123 "; Echo htmlentities ($ str); // string escape <> & '"avoids conflicts with html identifiers so that they can be displayed on the html browser. The result is:" <br> 123 ". Echo "<br> "; ?>