Q week: Please enter the first letter of the week to determine what day of the week, if the first letter of the same, then continue to determine the second letter.

#include <stdio.h>

void main() {
    char letter;
    printf("Please enter the first letter:\n");
    while ((letter = getchar()) != 'Y') {
        switch (letter) {
            case 's':
                printf("Please enter the second letter:\n");
                if ((letter = getchar()) == 'a') {
                    puts("saturday\n");
                } else if ((letter = getchar()) == 'u') {
                    puts("sunday\n");
                } else {
                    puts("data error.");
                }
                break;
            case 't':
                printf("Please enter the second letter:\n");
                if ((letter = getchar()) == 'u') {
                    puts("tuesday\n");
                } else if ((letter = getchar()) == 'h') {
                    puts("thursday\n");
                } else {
                    puts("data error.");
                }
                break;
            case 'm':
                puts("monday\n");
                break;
            case 'w':
                puts("wednesday\n");
                break;
            case 'f':
                puts("friday\n");
                break;
            default:
                puts("data error.");
        }
    }
}