C语言中ctype.h文件常用函数总结

1.isalpha：判断字符是不是英文字母： 

/* isalpha example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="C++";
  while (str[i])
  {
    if (isalpha(str[i])) printf ("character %c is alphabetic\n",str[i]);
    else printf ("character %c is not alphabetic\n",str[i]);
    i++;
  }
  return 0;
}

输出：

character C is alphabetic
character + is not alphabetic
character + is not alphabetic

2.isdigit：判断是不是数字

/* isdigit example */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string>

using namespace std;
int main ()
{
  //char str[]="1776ad";
  string s = "1222asd44asfd";
  int num = 0;
  int i = 0;
  for(auto c : s){
     if (isdigit(c))
     {
        num++;
     }
  }
  printf("%d",num);
  return 0;
}

输出：6

3.islower ：判断小写字母

/* islower example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="Test String.\n";
  char c;
  while (str[i])
  {
    c=str[i];
    if (islower(c)) c=toupper(c);
    putchar (c);
    i++;
  }
  return 0;
}

输出：

TEST STRING.

4.isupper ：判断大写字母

/* isupper example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="Test String.\n";
  char c;
  while (str[i])
  {
    c=str[i];
    if (isupper(c)) c=tolower(c);
    putchar (c);
    i++;
  }
  return 0;
}

输出：

test string.

5.toupper():转换成大写

6.tolower():转换成小写 

标签：函数,int,character,ctype,C语言,char,str,alphabetic,include
来源： https://blog.csdn.net/zpznba/article/details/88971447