一：设计思路：
1.随机产生2个0到99之间的随机数，用作运算数；随机产生1个0到3之间的数，分别代表运算符+，-，*,/。
2.if....else....语句控制输出的算式，for循环输出30道题。
3.当运算符为“/”号时，需要判断除数是否为0，如果为0，则循环次数加一。
4.为了保证随机种子的不同，需要用到srand(time(NULL))函数。
5.循环遍历已经出过的题，查看是否有重题。
二：源程序：
#include<iostream>
using namespace std;
#include<string>
#include<time.h>
void main()
{
srand(time(NULL));
string mark;
int key_one;
int key_two;
int dividend1,divider1,dividend2,divider2;
string result[30];
for(int i=0;i<30;i++)
{
key_one=rand()%4;
key_two=rand()%2;
if(key_two==0)
{
dividend1=rand()%100;
divider1=rand()%100;
if(key_one==0)
{
cout << dividend1 << "+" << divider1 << "= ?"<<endl;
result[i]=dividend1 + divider1;
}
else if(key_one==1)
{
cout << dividend1 << "-" << divider1 << "= ?"<<endl;
result[i]=dividend1 - divider1;
}
else if(key_one==2)
{
cout << dividend1 << "*" << divider1 << "= ?"<<endl;
result[i]=dividend1 * divider1;
}
else if(key_one==3)
{
if(divider1==0)
{
i++;
break;
}
cout << dividend1 << "/" << divider1 << "= ?"<<endl;
result[i]="dividend/divider";
}
else
cout << "Please try again!" << endl;
}
if(key_two==1)
{
dividend1=rand()%100;
divider1=rand()%100;
dividend2=rand()%100;
divider2=rand()%100;
if(key_one==0)
{
cout << dividend1 << "/" <<divider1 << "+" <<dividend2<<"/" <<divider2<< "= ?"<<endl;
}
else if(key_one==1)
{
cout << dividend1 << "/" <<divider1 << "-" <<dividend2<<"/" <<divider2<< "= ?"<<endl;
}
else if(key_one==2)
{
cout <<"("<< dividend1 << "/" <<divider1 <<")"<< "*" <<"("<<dividend2<<"/" <<divider2<<")"<< "= ?"<<endl;
}
else if(key_one==3)
{
if(divider1==0||divider2==0)
{
i++;
break;
}
cout <<"("<< dividend1 << "/" <<divider1 <<")"<< "/" <<"("<<dividend2<<"/" <<divider2<<")"<< "= ?"<<endl;
}
else
cout << "Please try again!" << endl;
}
}
}
三：结果截图：
四：上课未按时完成作业的原因：
没有认真思考问题，盲目的敲代码，思路不清晰，只是想一步写一步，一旦出错只能从头查找修改，浪费了大量的时间。