字母大小写转换 C

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

int main()
{
    char ch;
    printf("press a key and then press enter:");
    ch = getchar();
    if(ch <= 'z' && ch >='a')
        ch = ch - 32 ;
    else if(ch <= 'Z' && ch >= 'A')
        ch = ch +32;
    putchar(ch);
    putchar('\n');
    return 0;
}