题目要求： • 能自动生成小学四则运算题目（注意是给小学生用的） •除了整数外，还要支持真分数的四则运算

题目分析：1.由于是给小学生用的，所以要求运算的时候不能有负数，因此，减法运算时，前面的数一定要大于后面的数。

              2.除法运算的规则，分母不能为0。

              3.题目要求支持真分数，由真分数的概念知，分子不能大于分母的数。

              4.因为题目要求是随机30道题，所以运用随机生成数函数srand（）和rand（）。

 #include<stdio.h>
 #include<Windows.h>
 #include<time.h>
  void main()
  {
      int a, b, c, d,i,m,n;
      float p, q;
     srand(unsigned( time(NULL)));
      for (i = 0; i < 30; i++)
     {
        a = rand() % 100;
        b = rand() % 100;
        c = rand() % 5;
         switch (c)
         {
         case 0: printf("%d + %d =\n", a, b);
             break;
         case 1:if (a < b)
         {
                    d = a;
                    a = b;
                    b = d;
         }
                printf("%d - %d =\n", a, b);
                break;
         case 2:printf("%d * %d =\n", a, b);
             break;
         case 3:
             while (b == 0)
             {
                 b = rand() % 100;
             }
             printf("%d / %d =\n", a, b);
             break;
         case 4:
             a = rand() % 100;
             b = rand() % 100;
             m = rand() % 100;
             n = rand() % 100;
             c = rand() %4 ;
             while (b == 0)
             {
                 b = rand() % 100;
             }
             while (n == 0)
             {
                 n = rand() % 100;
             }
             if (a > b)
             {
                d = a;
                 a = b;
                 b = d;
             }
             if (m > n)
             {
                 d = m;
                 m = n;
                 n = d;
             }
             switch (c)
             {
            case 0:printf("%d/%d + %d/%d =\n", a, b, m, n);
                 break;
            case 1:
                 p = (float)a / (float)b;
                 q = (float)m / (float)n;
                 if (p < q)
                 {
                     d = a;
                     a = m;
                     m = d;
                     d = b;
                     b = n;
                     n = d;
                 }
                 printf("%d/%d - %d/%d =\n", a,b,m,n);
                 break;
             case 2:printf("%d/%d * %d/%d =\n", a, b, m, n);
                 break;
             case 3:
                 a = rand() % 100;
                 b = rand() % 100;
                 m = rand() % 100;
                 n = rand() % 100;
                 c = rand() % 4;
                 while (m == 0)
                 {
                     m = rand() % 100;
                 }
                 printf("%d/%d / %d/%d =\n", a, b, m, n);
                 break;
             }
        }
     }
     system("pause");
 }

四则运算