PHP example of randomly generating random numbers of letters

In many system environments, letters and various encodings are used. The following describes how to use php to randomly generate random numbers of letters. if you are interested, you can understand that in many system environments, you will use letters and combinations of various encodings, the following code is very practical.

$ Num is composed of several letters.

The $ s letter is case-sensitive. you can set it to uppercase or lowercase.
The code is as follows:
Function makecode ($ num = 4 ){
$ Re = ";
$ S = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy ';
While (strlen ($ re) <$ num ){
$ Re. = $ s [rand (0, strlen ($ s)-1)]; // randomly generates a character from $ s
}
Return $ re;
}