#include <stdio.h>
#include <ctype.h>
int main()
{
char character;
   do {
        printf("Press r: ");
        scanf("%c", &character);
        character = tolower(character);
        switch (character) {
            case 'r':
                printf("Valid\n");
                break;
            default:
                printf("Not valid\n");
                break;
        }
    }while (character != 'r');
    return 0;
}