有没有大老帮我解决一下下面图片的内容

代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void menu()
{
    system("cls");
    printf("************************************\n");
    printf("*      欢迎使用小学数学测试系统    *\n");
    printf("*    1.加法                        *\n");
    printf("*    2.减法                        *\n");
    printf("*    3.乘法                        *\n");
    printf("*    4.除法                        *\n");
    printf("*    0.退出                        *\n");
    printf("************************************\n");
    printf("请输入选项：");
}
//生成1-fw之间的随机数
void rand(int fw,int *a,int* b)
{
    int t;
    *a = rand()%fw+1;
    *b = rand()%fw+1;
    //保证a大于等于b
    if(*a < *b)
    {
        t=*a;
        *a =*b;
        *b = t;
    }
}

int main()
{
    int opt;
    int a,b,res;
    int njia=0,njiaright = 0;
    int njian=0,njianright=0;
    int ncheng=0,nchengright=0;
    int nchu=0,nchuright=0;
    int flag = 1;
    srand((unsigned int)time(NULL));
    while(flag)
    {
        menu();
        scanf("%d",&opt);
        switch(opt)
        {
        case 1:
            njia++;
            rand(50,&a,&b);
            printf("%d + %d = ",a,b);
            scanf("%d",&res);
            if(res == a+b)
            {
                njiaright++;
                printf("正确！\n");
            }else
                printf("错误！\n");
            break;
        case 2:
            njian++;
            rand(50,&a,&b);
            printf("%d - %d = ",a,b);
            scanf("%d",&res);
            if(res == a-b)
            {
                njianright++;
                printf("正确！\n");
            }else
                printf("错误！\n");
            break;
        case 3:
            ncheng++;
            rand(50,&a,&b);
            printf("%d -*%d = ",a,b);
            scanf("%d",&res);
            if(res == a*b)
            {
                nchengright++;
                printf("正确！\n");
            }else
                printf("错误！\n");
            break;
        case 4:
            nchu++;
            rand(50,&a,&b);
            printf("%d / %d = ",a,b);
            scanf("%d",&res);
            if(res == a/b)
            {
                nchu++;
                printf("正确！\n");
            }else
                printf("错误！\n");
            break;
        case 0:
            flag = 0;
            break;
        }
    }
    printf("总题数：%d   正确率：%d%%\n",(njia+njian+ncheng+nchu),100*(njiaright+njianright+nchengright+nchuright)/(njia+njian+ncheng+nchu));
    printf("加法个数：%d   正确个数：%d\n",njia,njiaright);
    printf("减法个数：%d   正确个数：%d\n",njian,njianright);
    printf("乘法个数：%d   正确个数：%d\n",ncheng,nchengright);
    printf("除法个数：%d   正确个数：%d\n",nchu,nchuright);
    return 0;
}