C语言大作业小学生随机出题测试计分

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

int test();
int checknum(int a, int b);
int checkresult(int x);

int a = -1, b, c, x;
static int k = 0, grade;

void main() {
    printf("请作答下列十道题，回车键开始开始作答！！！");
    getchar();
    do {
        int i = test();
        if (i == -1) {
            break;
        }
        else if (checkresult(i) == 0) {
            a = -1;
        }
    } while (k);
    getchar(); getchar(); getchar();
}

int test() {
    srand((unsigned int)time(NULL));
    while (checknum(a, b) == 0)
    {
        a = rand() % 51;
        b = rand() % 51;
        c = rand() % 2;
    }
    k++;
    if (k == 11) {
        printf("答题结束，您本次测试总分是 %d ，谢谢", grade);
        return -1;
    }
    else if (c == 0) {
        printf("第%d题:  %d+%d=", k, a, b);
        return a + b;
    }
    else if (c == 1) {
        printf("第%d题:  %d-%d=", k, a, b);
        return a - b;
    }
    return -1;
}
int checknum(int a, int b) {
    if ((a + b) > 50 || (a - b) < 0 || a > 50 || b > 50 || a < 0 || b < 0) {
        return 0;
    }
    return 1;
}
int checkresult(int result) {
    int i;
    for (i = 1; i++; i <= 3) {
        scanf_s("%d", &x);
        if (x != result) {
            if (i == 4) {
                if (c == 0) {
                    printf("三次回答错误，正确答案是%d，请回答下一题\n", a + b);
                }
                else {
                    printf("三次回答错误，正确答案是%d，请回答下一题\n", a - b);
                }
                return 0;
            }
            printf("回答错误，请重新计算并输入结果：");
        }
        else {
            switch (i) {
            case 2:
                grade += 10;
                break;
            case 3:
                grade += 7;
                break;
            case 4:
                grade += 5;
                break;
            default:
                grade += 0;
                break;
            }
            return 0;
        }
    }
    return 0;
}