#include<stdio.h>
void main()
{
	char rui[128]="";
	int i;
	printf("请输入想要转换的字符：");
	fgets(rui,sizeof(rui),stdin);
	for(i=0;i<128;i++)
	{
		if((rui[i]>=65 && rui[i]<=90) || (rui[i]>=97 && rui[i]<=122))
		{
		if(rui[i]>=65 && rui[i]<=90)
			rui[i]=rui[i]+32;
		else 
			rui[i]=rui[i]-32;
		}
	}
	printf("转换结果：%s",rui);
}

结果：

标签：char,rui,小写字母,大写,大写字母,int,65,&&
来源： https://blog.csdn.net/qq_42783177/article/details/110764156