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标题: 新手写的《c prime plus》第八章的一个习题，大神指点下 [打印本页]

作者: xiaowh00 时间: 2012-07-27 11:13
标题: 新手写的《c prime plus》第八章的一个习题，大神指点下
/* author: xiaowh00 */
/* date: 2012-7-27 */

#include <stdio.h>

void menu(void); // print munu
void get_input(char); // get operation and operand
float get_float(void); // get float number
void operate(float,float,char); // operate (+-*/)
void flush(void); // flush keyboard

int main(void)
{
      char ch; // choice

      menu();
      while(scanf("%c",&ch)==1 && ch!='q')
      {
            if(ch=='a' || ch=='s' || ch=='m' || ch=='d')
            {
                     get_input(ch);
                     menu();
                     flush();
            }
            else
            {
                     printf("wrong operation\n");
                     menu();
                     flush();
            }
      }

      printf("Bye.\n");

      return 0;
}

void menu(void)
{
      printf("Enter the operation of your choice:\n");
      printf("a. add       s. subtract\n");
      printf("m. multiply    d. divide\n");
      printf("q. quit\n");
}

void flush(void)
{
      int ch;
      while((ch=getchar())!=EOF && ch!='\n')
            ;
}
void get_input(char op)
{
      float op1,op2;

      printf("Enter first number: ");
      op1=get_float();
      printf("Enter second number: ");
      op2=get_float();

      while((op=='d' || op=='s') && op2==0)
      {
            printf("Enter a number other than 0: ");
            op2=get_float();
      }
      operate(op1,op2,op);

}

float get_float(void)
{
      float f;
      int ch;

      while(scanf("%f",&f)!=1)
      {
            while((ch=getchar())!='\n')
                     putchar(ch);
            printf(" is not an number.\n");
            printf("Please enter a number,such as 2.5,-1.78E8,or 3: ");
      }
      return f;
}

void operate(float op1,float op2,char op)
{
      switch(op)
      {
            case 'a' : printf("%.2f + %.2f = %.2f\n",op1,op2,op1+op2);
                        break;
            case 's' : printf("%.2f - %.2f = %.2f\n",op1,op2,op1-op2);
                        break;
            case 'm' : printf("%.2f * %.2f = %.2f\n",op1,op2,op1*op2);
                        break;
            case 'd' : printf("%.2f / %.2f = %.2f\n",op1,op2,op1/op2);
                        break;
            default : printf("there must be some error!\n");
                        break;
      }
}

作者: pmerofc 时间: 2012-07-27 11:28
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作者: pmerofc 时间: 2012-07-27 11:29
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作者: xiaowh00 时间: 2012-07-27 11:29
Write a program that shows you a menu offering you the choice of addition, subtraction, multiplication, or division. After getting your choice, the program asks for two numbers, then performs the requested operation. The program should accept only the offered menu choices. It should use type float for the numbers and allow the user to try again if he or she fails to enter a number. In the case of subtraction, the program should prompt the user to enter a new value if 0 is entered as the value for the second number. A typical program run should look like this:

Enter the operation of your choice:

a. add          s. subtract

m. multiply    d. divide

q. quit

a

Enter first number: 22.4

Enter second number: one

one is not an number.

Please enter a number, such as 2.5, -1.78E8, or 3: 1

22.4 + 1 = 23.4

Enter the operation of your choice:

a. add          s. subtract

m. multiply    d. divide

q. quit

d

Enter first number: 18.4

Enter second number: 0

Enter a number other than 0: 0.2

18.4 / 0.2 = 92

Enter the operation of your choice:

a. add          s. subtract

m. multiply    d. divide

q. quit

q

Bye.

回复 2# pmerofc

作者: xiaowh00 时间: 2012-07-27 11:32
首先谢谢你的恢复哈！
就是清空键盘缓冲区，本来使用fflush(),但是我用fflush()发现在gcc下没效果，查了scanf()的百度百科，这个在gcc下不能用，就自己写了一个flush()

回复 3# pmerofc

作者: pmerofc 时间: 2012-07-27 11:39
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作者: xiaowh00 时间: 2012-07-27 11:44
恩，确实可以简化成这样

pmerofc 发表于 2012-07-27 11:39
回复 1# xiaowh00 明显应该写为

作者: pmerofc 时间: 2012-07-27 11:47
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作者: xiaowh00 时间: 2012-07-27 11:52
逗号表达式的用法，我怎么没想到呢，不过这样连起来写是简洁了，while这一句有点复杂
还有一个问题就是我的格式化输出的问题，比如输入1.2+1 怎么样实现输出1.2+1 我用的固定的.2%f ，如何根据输入的数据自动判断如何输出啊？
回复 8# pmerofc

作者: pmerofc 时间: 2012-07-27 12:03
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