C语言实现大小写转换的三种方法

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实现大小写转换的三种方法

方法一：

#include<stdio.h>
#include<stdlib.h>

int main()
{
 char str[] = "AbCdEf";
 char c;
 int i = 0;
 while (str[i] != '\0')
 {
  c = str[i];
  if (c >= 'A' && c <= 'Z')
  {
   c = c + 32;
  }
  else if (c >= 'a' && c <= 'z')
  {
   c = c - 32;
  }
      printf("%c",c);
  i++;
 }
 printf("\n");
 system("pause");
 return 0;
}

运行结果如下：

方法二： 

#include<stdio.h>
#include<stdlib.h>

int main()
{
 char str[] = "AbCdEf";
 char c;
 int i = 0;
 while (str[i] != '\0')
 {
  c = str[i];
  if (c >= 'A' && c<='Z' || c>='a' && c <= 'z')
  {
   c ^= 32;
  }
  printf("%c", c);
  i++;
 }
 printf("\n");
 system("pause");
 return 0;
}

运行结果如下：

方法三：

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

int main()
{
 char str[] = "AbCdEf";
 char c;
 int i = 0;
 while (str[i] != '\0')
 {
  c = str[i];
  if (isupper(c))
  {
   c = tolower(c);
  }
  else if (islower(c))
  {
   c = toupper(c);
  }
  printf("%c", c);
  i++;
 }
 printf("\n");
 system("pause");
 return 0;
}

运行结果如下：

小写转大写封装 ：

​uint8_t low2UpperChar(uint8_t *in, int inlen, uint8_t *out) {
	char c;
	for (int i = 0; i < inlen; i++)
	{
		c = in[i];
		if ('a' <= c && c <= 'z')
		{
			out[i] = c - 32;
		}
		else
		{
			out[i] = c;
		}
	}
	return 0;
}

​