第一次作业

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
main()
{
	int choice;
	int a,b,c;
	srand((unsigned) time(NULL));

	printf("\n\n-------------每天一练-------------");
    printf("\n1.加法运算:");
	printf("\n2.减法运算:");
	printf("\n3.乘法运算:");
	printf("\n4.除法运算:");
	printf("\n5.退出练习:");
	while(1)
	{
	printf("\n\n请选择所需要的练习:");
	scanf("%d",&choice);
	switch(choice)
	{
	case 1:
		a=rand()%99;
	    b=99-a;
		printf("\n\n%d+%d=?",a,b);
		break;
	case 2:
		a=rand()%99;
	    b=99-a;
		printf("\n\n%d-%d=?",a,b);
		break;
	case 3:
		a=rand()%10;
	    b=50-a;
		printf("\n\n%d*%d=?",a,b);
		break;
	case 4:
		a=rand()%50;
	    b=100-a;
		printf("\n\n%d/%d=?",a,b);
		break;
	case 5:
		printf("\n\n欢迎使用每课一练!!");
		exit(0);
		break;
	default:
		printf("输入错误，请重新输入(1-5):");	
	}
	}
}