C语言实例51：读写字符

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

int main(int argc, char *argv[])
{
    char ch;
    printf("Please enter some text (input a point to quit).\n");
        do{
        ch = getchar();
        if(islower(ch))
            ch = toupper(ch);
        else
            ch = tolower(ch);
        putchar(ch);
    }while(ch != '.');
    system("pause");
    return 0;
}