题目：二柱子将做好的项目交给了老师，几天后又得到了新的需求：
作业要求1、实现在线答题。
2、答题结束后，可以判断对错。
3、并将错题的结果保存起来。
设计思路：整理要求，利用srand(time(NULL));来进行循环，来计算题目数量，选择公式。还要控制 数据范围，运算加减乘除法四则运算，判断负数和真分数并进行计算，最后判断正错和统计正错，然后保存错题。
程序代码：
#include<iostream.h>
#include<stdlib.h>
#include<time.h>
void boom()
{
float x,y;
int z,t;
int first_num,second_num,third_num,fourth_num;
srand(time(NULL));
int n;
float k;
float d;
float daan[100];
int zq=0;
int cw=0;
cout<<"需要列出多少到数学题?"<<endl;
cin>>n;
for(int i=0;i<n;i++)
{
z=rand()%4;
first_num=rand()%10;
second_num=rand()%10;
third_num=rand()%10;
fourth_num=rand()%10;
if (second_num==1)
{
x=(float)first_num;
}
else if(first_num>second_num)
{
t=first_num;
first_num=second_num;
second_num=t;
}
x=(float)first_num/second_num;
if (fourth_num==1)
{
y=(float)third_num;
}
else if(third_num>fourth_num)
{
t=third_num;
third_num=fourth_num;
fourth_num=t;
}
y=(float)third_num/fourth_num;
z=rand()%4;
switch(z)
{
case 0:
cout<<i+1<<"、 "<<first_num<<"/"<<second_num<<"+"<<third_num<<"/"<<fourth_num<<"="<<" ";
daan[i+1]=x+y;
break;
case 1:
cout<<i+1<<"、 "<<first_num<<"/"<<second_num<<"-"<<third_num<<"/"<<fourth_num<<"="<<" ";
daan[i+1]=x-y;
break;
case 2:
cout<<i+1<<"、 "<<first_num<<"/"<<second_num<<"*"<<third_num<<"/"<<fourth_num<<"="<<" ";
daan[i+1]=x*y;
break;
case 3:
if(y!=0)
{
cout<<i+1<<"、 "<<first_num<<"/"<<second_num<<"÷"<<third_num<<"/"<<fourth_num<<"="<<" ";
}
else
{
i=i-1;
}
daan[i+1]=(float)x/y;
break;
}
if((i+1)%3==0)
{
for(int c=0;c<=1;c++)
{
cout<<endl;
}
}
if((i+1)==n)
{
cout<<endl;
}
}
for(i=1;i<=n;i++)
{
cout<<"请作答:"<<endl;
cout<<i<<"、";
cin>>d;
if(d==daan[i])
{
cout<<"回答正确！"<<endl;
cout<<endl;
zq=zq+1;
}
else
{
cout<<"回答错误，正确答案为："<<" "<<daan[i]<<endl;
cout<<endl;
cw=cw+1;
}
}
k=(float)zq/n;
cout<<"回答正确的数量为："<<" "<<zq<<"个"<<endl;
cout<<"回答错误的数量为："<<" "<<cw<<"个"<<endl;
cout<<"正确率为："<<" "<<k<<endl;
}
int main()
{
boom();
main();
return 0;
}