请求帮助，一道练习题！
c primer plus第5版 8-8的一个练习8．编写一个程序，显示一个菜单，为您提供加法、减法、乘法或除法的选项。获得您的选择后，该程序请求两个数，然后执行您选择的操作。该程序应该只接受它所提供的菜单选项。它应该使用float类型的数，并且如果用户未能输入数字应允许其重新输入。在除法的情况中，如果用户输入O作为第二个数，该程序应该提示用户输入一个新的值。一个典型的程序运行应该如下所示：我实现除法输入第二个数的时候，有问题！其他的似乎还比较正常！各位帮我看看吧。谢谢了！
Enter the operation of your choice:
a. add s. subtract
m. multiply d. divide
q. quic
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
Enter first number: 18.4
Enter second number: O
Enter a number other than 0: 0.2 //我实现除法输入第二个数的时候，有问题！其他的似乎还比较正常！各位帮我看看吧。谢谢了！
18.4 / 0.2 = 92
Enter the operation of your choice:
a. add s. subtract
m. multiply d. divide
q. quit
q
Bye.
程序代码：#include <STDIO.H>
#include <CTYPE.H>
void menu(void);
void add(void);
void substract(void);
void multiply(void);
void divide(void);
char get_choice(void);
char get_first(void);
float get_float(void);
int main(void)
{
int choice;
while ((choice = get_choice()) != 'q')
{
switch (choice)
{
case 'a': add();
break;
case 's': substract();
break;
case 'm': multiply();
break;
case 'd': divide();
break;
default : puts("error");
break;
}
}
puts("Bye");
return 0;
}
void menu(void)
{
puts("Enter the operation of your choice:");
printf("a. add s. subtract\n");
printf("m. multiply d. divide\n");
puts("q. quit");
}
void add(void)
{
float firstnumber, secondnumber;
puts("Enter first number:");
firstnumber = get_float();
puts("Enter second number:");
secondnumber = get_float();
printf("%.1f + %.1f = %.1f\n", firstnumber, secondnumber, firstnumber + secondnumber);
}
void substract(void)
{
float firstnumber, secondnumber;
puts("Enter first number:");
firstnumber = get_float();
puts("Enter second number:");
secondnumber = get_float();
printf("%.1f - %.1f = %.1f\n", firstnumber, secondnumber, firstnumber - secondnumber);
}
void multiply(void)
{
float firstnumber, secondnumber;
puts("Enter first number:");
firstnumber = get_float();
puts("Enter second number:");
secondnumber = get_float();
printf("%.1f * %.1f = %.1f\n", firstnumber, secondnumber, firstnumber * secondnumber);
}
void divide(void)
{
float firstnumber, secondnumber;
int ch;
puts("Enter first number:");
firstnumber = get_float();
puts("Enter second number:");
secondnumber = get_float();
while((secondnumber = get_float()) == 0)
{
do
{
ch = getchar();
} while (isspace(ch));
puts("Enter a number more than 0:");
continue;
}
printf("%.1f / %.1f = %.1f\n", firstnumber, secondnumber, firstnumber / secondnumber);
}
char get_choice(void)
{
int ch;
menu();
ch = get_first();
//while ( (ch < 'a' || ch > 's') && ch != 'q')
while(ch != 'a' && ch != 's' && ch != 'm' && ch != 'd' && ch != 'q')
{
printf("Please respond with a, d, s, m, or q.\n");
ch = get_first();
}
return ch;
}
char get_first(void)
{
int ch;
do
{
ch = getchar();
} while (isspace(ch));
while (getchar() != '\n')
continue;
return ch;
}
float get_float(void)
{
int ch;
float float_num;
while(scanf("%f", &float_num) != 1)
{
while((ch = getchar()) != '\n')
putchar(ch);
printf("is not an number.\n");
printf("enter a number,such as 2.5,-1.78E8 or 3:");
}
return float_num;
}
我实现除法输入第二个数的时候，有问题！其他的似乎还比较正常！各位帮我看看吧。谢谢了！[ 本帖最后由 迷途的菜鸟 于 2012-8-17 14:06 编辑 ]
