C Primer Plus第六版 第八章编程练习

最后一题

#include <stdio.h>
 
char choice(void);
float first_number(void);
float second_number(void);
float add(float a,float b);
float multiply(float a,float b);
float subtract(float a,float b);
float divide(float a,float b);
 
int main(void)
{
	float a,b;
	float sum,multi,sub,div;
	char ch = 0;
	
	while((ch = choice()) != 'q')
	{
		a = first_number();
		b = second_number();
		
		switch(ch)
			{
				case 'a':
					sum = add(a,b);
					break;
				case 'm':
					multi = multiply(a,b);
					break;
				case 's':
					sub = subtract(a,b);
					break;
				case 'd':
					if (b == 0)
					{
						printf("Enter a number other than 0:");
						scanf("%f",&b);
					}
					div  = divide(a,b);
					break; 
			}
					
		
		if (ch == 'a')
			printf("The sum of the two numbers is %f.\n",sum);
		else if (ch == 'm')
			printf("The multiply of the two numbers is %f.\n",multi);
		else if (ch == 'd')
			printf("The divide of the two numbers is %f.\n",div);
		else if (ch == 's')
			printf("The subtract of the two numbers is %f.\n",sub);
			
		while(getchar() != '\n');
	}
	printf("Bye!");
		
	return 0;
		
}
 
 
char choice(void)
{
	char cho;
	
	printf("Enter the operation of your choice:\n");
	printf("a.add			s.subtract\n");
	printf("m.multiply		d.divide\n");
	printf("q.quit\n");
	
	while((cho = getchar()) && cho != 'a' && cho != 'm' && cho != 's' && cho != 'd' && cho != 'q')
		{
			printf("Please enter again, enter a, m, s, d or q:");
			while(getchar() != '\n');
		}
	
	return cho;
}
 
 
float first_number(void)
{
	float first_num;
	char num;
	
	printf("Enter fisrt number:");
	
	while(scanf("%f",&first_num) != 1)  //如果输入不是数字，则scanf不会读取，会放在输入缓存等待读取，就可以用下面的getchar来读取这个字符 
	{
		while((num = getchar()) != '\n')
			putchar(num);
		printf(" is not an number.\n");
		printf("Please enter a number, such as 2.5, -1.78E8, or 3:");	
	}
	
	return first_num;
}
 
 
float second_number(void)
{
	float second_num;
	char num;
	
	printf("Enter second number:");
	
	while(scanf("%f",&second_num) != 1)
	{
		while((num = getchar()) != '\n')
			putchar(num);
		printf(" is not an number.\n");
		printf("Please enter a number, such as 2.5, -1.78E8, or 3:");		
	}
	
	return second_num;
}
 
 
float add(float a,float b)
{
	float sum;
	
	sum = a + b;
	
	return sum;
}
 
float multiply(float a,float b)
{
	float multi;
	
	multi = a * b;
	
	return multi;
}
 
float subtract(float a,float b)
{
	float sub;
	
	sub = a - b;
	
	return sub;
}
 
float divide(float a,float b)
{
	float div;
	
	div = a / b;
	
	return div;
}