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：
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
18.4 / 0.2 = 92
Enter the operation of your choice:
a. add s. subtract
m. multiply d. divide
q. quit
q
Bye.
#include<stdio.h> #include<ctype.h> float get_float(void); char get_first(void); int main(void) { char select; float num1,num2; while(1) { printf("Enter the operation of your choice:\n"); printf("a.add s.subtract:\n"); printf("m.multiply d.divide\n"); printf("q.quit\n"); select = get_first(); if( select != 'a' && select != 's' && select != 'm' && select != 'd') { printf("Bye.\n"); break; } printf("Enter first number:"); num1 = get_float(); printf("Enter second number:"); num2 = get_float(); while( select == 'd' && num2 == 0) { printf("Enter a number other than 0:"); num2 = get_float(); } switch(select) { case 'a': printf("%.2f + %.2f = %.2f\n",num1, num2, num1 + num2); break; case 's': printf("%.2f - %.2f = %.2f\n",num1, num2, num1 - num2); break; case 'm': printf("%.2f * %.2f = %.2f\n",num1, num2, num1 * num2); break; case 'd': printf("%.2f / %.2f = %.2f\n",num1, num2, num1 / num2); break; default : break; } } return(0); } float get_float(void) //得到一个合适的浮点数，滤除非法数 { float num; char str[40]; while(scanf("%f",&num)!=1) { gets(str); printf("%s is not a number.\n",str); printf("Please enter a numbe, such as 2.5, -1.78E8, or 3:"); } while ( getchar() != '\n'); return num; } char get_first(void) //得到字符串中的第一个字符，滤除其他字符 { int ch; while( isspace( ch = getchar() ) ); while ( getchar() != '\n'); return ch; }