C语言isalnum()函数：判断字符是否为英文字母或数字
头文件：
#include <ctype.h>
isalnum() 用来判断一个字符是否为英文字母或数字，相当于 isalpha(c) || isdigit(c)，其原型为：
int isalnum(int c);
【参数】c 为需要检测的字符。
【返回值】若参数c 为字母或数字，若 c 为 0 ~ 9 a ~ z A ~ Z 则返回非 0，否则返回 0。
注意，isalnum()为宏定义，非真正函数。
【实例】找出str 字符串中为英文字母或数字的字符。
#include <ctype.h>
main(){
char str[] = "123c@#FDsP[e?";
int i;
for (i = 0; str[i] != 0; i++)
if(isalnum(str[i]))
printf("%c is an alphanumeric character\n", str[i]);
}
输出结果：
1 is an apphabetic character 2 is an apphabetic character 3 is an apphabetic character c is an apphabetic character F is an apphabetic character D is an apphabetic character s is an apphabetic character P is an apphabetic character e is an apphabetic character
C语言isalpha()函数：判断字符是否为英文字母
头文件：
#include <ctype.h>
isalpha() 用来判断一个字符是否是英文字母，相当于 isupper(c)||islower(c)，其原型为：
int isalpha(int c);
【参数】c 为需要被检测的字符。
【返回值】若参数c 为英文字母（a ~ z A ~ Z），则返回非 0 值，否则返回 0。
注意，isalpha() 为宏定义，非真正函数。
【实例】找出str 字符串中为英文字母的字符。
#include <ctype.h>
main(){
char str[] = "123c@#FDsP[e?";
int i;
for (i = 0; str[i] != 0; i++)
if(isalpha(str[i]))
printf("%c is an alphanumeric character\n", str[i]);
}
执行结果：
c is an apphabetic character F is an apphabetic character D is an apphabetic character s is an apphabetic character P is an apphabetic character e is an apphabetic character
