C语言输入小写输出大写，输入大写输出小写

#include<stdio.h>
#include<stdlib.h>
int main(){
int ch = 0;
printf(“输入一个字符!\n”);
while ((ch = getchar()) != 0){ //循环中ch均表示为ASCII值
if (ch >= ‘a’&&ch <= ‘z’){
printf("%c", ch - 32);
}
if (ch >= ‘A’ && ch <= ‘Z’){
printf("%c", ch + 32);
}
if (ch >= ‘0’&&ch <= ‘9’){
printf(“无效输入!”);
}
}
system(“pause”);
return 0;
}