学习 while ((ch = getchar()) != EOF)，islowe tolower toupper

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>


int main()
{
    int ch = 0;
    while ((ch = getchar()) != EOF)
    {
        if (islower(ch))
        {
            printf("%c\n", toupper(ch));
        }
        else
        {
            printf("%c\n", tolower(ch));
        }
        getchar();
    }
    return 0;
}