像阿超那样，花20分钟写一个能自动生成小学生四则运算题目的程序。

主要函数：
char getSignal();                      //获取随机运算符函数
int random(double,double);             //获取随机数函数
int getResult(int,int,char);           //结果计算函数
int takeTest();                        //题目生成函数
②主函数
void main() 
{
         int n,a,right=0;
         double percent;
         printf("Please enter the number of the test:");
         scanf("%d",&n);
         for(int i=0;i<n;i++)
         {
                   a=takeTest();
                   right=right+a;
         }
         printf("Powerful!\n");
         printf("The number of right:%d\n",right);
         percent=((double)right*100.00)/(double)n;
         printf("The percent of right:%0.2f %%\n",percent);
}
③获取随机运算符函数：
char getSignal()
{
    char signal[4]={'+','-','*','/'};
    srand((unsigned)time(NULL));
    return signal[rand()%4];
}
 ④获取随机数函数：
int random(double start, double end)
{
    return (int)(start+(end-start)*rand()/(RAND_MAX+ 1.0));
}
⑤结果计算函数：
int getResult(int num1,int num2,char signal)
{
    int res;
    switch(signal)
    {
    case '+':
        res=num1+num2;break;
    case '-':
        res=num1-num2;break;
    case '*':
        res=num1*num2;break;
    case '/':
        res=num1/num2;break;
    default:
        printf("运算符错误！\n");
    }
    return res;
}
⑥题目生成函数：
int takeTest()
{
    int get;
    int num1,num2,a;
    char signal;

    srand((unsigned)time(NULL));
    signal=getSignal();
    num1=random(0,1000);
    num2=random(1,1000);

    if(signal=='-')
    {
        if(num1<num2)
        {
            int temp;
            temp=num1;
            num1=num2;
            num2=temp;
        }
    }
    if(signal=='/')
    {
        if(num2==0)
        {
            int temp;
            temp=num1;
            num1=num2;
            num2=temp;
        }
    }
    printf("%d%c%d=",num1,signal,num2);
    scanf("%d",&get);
    fflush(stdin);   //清空输入缓冲区
    if(getResult(num1,num2,signal)==get)
        {
        printf("You're right!\n");
        a=1;
        }
    else
    {
        printf("It's wrong!\n");
        printf("The right answer is: %d\n",getResult(num1,num2,signal));
        a=0;
    }
    return a;
}