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

int question( int i)
{
	int a,b,j,m;
	 
	for( i = i;i<100;i++ ) 
  { 
    loop:
	{
		a=rand()%51;
		b=rand()%51;//rand()%100表示取50以内的随机数
		
		j=rand()%2;//j的值决定加减法
	}
	 if(j==0)
	 {
		 m=a+b;
		 if(m<=50)
		 {
			 printf("%d+%d=\n",a,b);
		 }
		 else
			 goto loop;
	 }

	 else
	 {
		 m=a-b;
		 if(m<=50&&m>=0)
		 {
			 printf("%d-%d=\n",a,b);
		 }
		 else
			 goto loop;

  } 
	 break;
}
	return m;
}

int main() 
{ 
	
	int modelanswer=0;
	int studentanswer=0;
	char str[20];
	int grade=0;
	int n;
	
   

    printf("\n");
    printf("============================================================\n");
	printf("====================50以内加减法测验系统====================\n");
    printf("============================================================\n");
	printf("\n");

	printf("请输入你的名字：\n");
	scanf("%s",str);
	printf("\n你好呀，%s小朋友，欢迎进入50以内加减法测验系统。\n",str);
	printf("每道题你有三次答题机会，如果三次机会结束则直接给出正确答案。\n");
	printf("\n测试结束后会给出你的成绩以及相应评级。\n");
	printf("\n");
	printf("======================要注意细心哦~=========================\n\n");

	for(n=1;n<11;n++)
	{
	printf("\n第%d道题：\n",n);
	modelanswer=question(n);
	
	printf("请输入答案：");
	scanf("%d",&studentanswer);
	if(studentanswer==modelanswer)
	{
		printf("回答正确，请继续加油哦。\n");
		grade=grade+10;
	}
	else
	{
		printf("回答错误，请好好思考。你还有两次机会。\n");
		printf("请输入答案：");
		scanf("%d",&studentanswer);

		if(studentanswer==modelanswer)
		{
			printf("回答正确，请继续加油哦。\n");
			grade=grade+7;
		}

		else
		{
			printf("回答错误，请好好思考。你还有一次机会。\n");
			printf("请输入答案：");
			scanf("%d",&studentanswer);

			if(studentanswer==modelanswer)
			{
				printf("回答正确，请继续加油哦。\n");
				grade=grade+5;
			}

			else
			{
				printf("回答错误。正确答案是：%d\n",modelanswer);
				grade=grade+0;
			}
		}
		}
	}
	

	if(grade>=90)
	{
		printf("\nSMART!\n");
	}

	if(grade<90&&grade>=80)
	{
		printf("\nGOOD!\n");
	}

	if(grade<80&&grade>=70)
	{
		printf("\nOK.\n");
	}

	if(grade<70&&grade>=60)
	{
		printf("\nPASS.\n");
	}

	if(grade<60)
	{
		printf("\nTRY AGAIN.\n");
	}

	printf("\n你的成绩是：%d\n",grade);

	return 0;
}