isalnum

 原型：extern int isalnum(int c);
 
 用法：#include <ctype.h>
 
 功能：判斷字符c是否為字母或數(shù)字
 
 說明：當(dāng)c為數(shù)字0-9或字母a-z及A-Z時，返回非零值，否則返回零。
 
 舉例：

      // isalnum.c
      
      #include <syslib.h>
      #include <ctype.h>
      main()
      {
        int c;
        
        clrscr();        // clear screen
        c='a';
        printf("%c:%s\n",c,isalnum(c)?"yes":"no");
        c='7';
        printf("%c:%s\n",c,isalnum(c)?"yes":"no");
        c='@';
        printf("%c:%s\n",c,isalnum(c)?"yes":"no");
        getchar();
        return 0;
      }