C语言实现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;}