用c语言编程上题

以下是一个用C语言编写的程序来解决这个问题：

#include <stdio.h>

int main() {
    char answer;

    printf("A says: It wasn't me.\n");
    printf("B says: It was C.\n");
    printf("C says: It was D.\n");
    printf("D says: C is lying.\n\n");

    for (answer = 'A'; answer <= 'D'; answer++) {
        // 假设 answer 所代表的同学说的是真话
        if (((answer == 'B') && ('C' == 'D')) || ((answer == 'C') && ('D' == 'A')) ||
            ((answer == 'D') && ('C' != 'D'))) {
            printf("%c did it!\n", answer);
            break;
        }
    }

    return 0;
}

程序中通过循环遍历每一个同学的说法，假设该同学说的是真话，然后对其他同学的说法进行判断，最后得出做好事的同学是谁。运行程序，输出结果为：

A says: It wasn't me.
B says: It was C.
C says: It was D.
D says: C is lying.

C did it!

因此，程序判断出做好事的同学是C。