C语言程序设计（第4版）课后练习题 第四章：数据的存储与运算

练习环境 windows 10
Visual Studio 2017

例子4.1输入两个学生a和b的成绩，输出其中高的成绩。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	float a, b, max;
	printf("please enter a and b:");
	scanf("%f,%f", &a, &b);
	if (a >= b)
		max = a;
	if (b > a)
		max = b;
	printf("max=%6.2f\n", max);
	return 0;
}

运行效果

优化程序
程序中用了两个if语句,先后进行了两次判断。其实可以只用一个if语句,在这个语句程序中用了两个if语句,先后进行了两次判断。其实可以只用一个if语句,在这个语句中包含一个else分支。可对程序修改如下:
这里顺带提及一下，为什么要减少if 语句，是因为到了数据结构那本书会提到算法的时间复杂度和空间复杂度，我们平时在写程序的时候也要时常考虑到这个问题，就是如何将程序在某个特定的环境下的算法最优。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	float a, b, max;
	printf("please enter a and b:");
	scanf("%f,%f", &a, &b);
	if (a >= b)
		max = a;
	else 
		max = b;
	printf("max=%6.2f\n", max);
	return 0;
}

例子4.2 输人3个成绩a,b,c,要求按由高到低的顺序输出。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	float  a, b, c, t;
	print("please enter a,b,c:");
	scanf("%f,%f,%f", &a, &b, &c);
	if(a<b)
	{
     
		t = a; a = b; b = t;
	}
	if (a < c)
	{
     
		t = a; a = c; c = t;
	}
	if(b<c)
	{
     
		t = b; b = c; c = t;
	}
	printf("%6.2f,%6.2f,%6.2f\n", a, b, c);
	return 0;
}

运行效果

例子4.2给出三角形的三个边长,求三角形的面积。

#define _CRT_SECURE_NO_WARNINGS
#include 
#include
int main()
{
     	
	double a, b, c, s, area;
	printf("Please enter a,b,c:");
	scanf("%lf,%lf,%lf", &a, &b, &c);
	if (a + b > c && b + c > a && c + a > b)
	{
     
		s = 0.5*(a + b + c);
		area = sqrt(s*(s - a)*(s - b)*(s - c));
		printf("area=%6.2f\n", area);
	}
	else
		printf("It is not a trilateral\n");
	return 0;
}

运行效果

例子4.4：为促销,对购买货物多的顾客有优惠:凡买50件以上(含50件)的优惠5%,买100 件以上(含100 件)的优惠7.5%,买300件以上(含300件)的优惠10%,买500件以上(含600件)的优惠15%。要求编程序,用户输入购买的数量和单价,程序输出应付货款。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int number;
	double cost, price, total;
	printf("plesase enter number and price:");
	scanf("%d,%lf", &number, &price);
	if (number >= 500)   //以下为6行嵌套语句
		cost = 0.15;
	else
		if (number >= 300)
			cost = 0.10;
		else
			if (number >= 100)
				cost = 0.075;
			else
				if (number >= 50)
					cost = 0.05;
				else cost = 0;
	total = number * price * (1 - cost);
	printf("total=%10.2f\n", total);
	return 0;
}

格式优化

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int number;
	double cost, price, total;
	printf("plesase enter number and price:");
	scanf("%d,%lf", &number, &price);
	if (number >= 500) cost = 0.15;
	else if (number >= 300) cost = 0.10;
	else if (number >= 100) cost = 0.075;
	else if (number >= 50) cost = 0.05;
	else cost = 0;
	total = number * price * (1 - cost);
	printf("total=%10.2f\n", total);
	return 0;
}

例4.5写程序,判断某一年是否闰年。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int year, leap;
	printf("Please enter a year:");
	scanf("%d", &year);
	if (year % 4 == 0)
	{
     
		if (year % 100 == 0)
		{
     
			if (year % 400 == 0)
				leap = 1;
			else
				leap = 0;
		}
		else
			leap = 1;
	}
	else
		leap = 0;
	if (leap)
		printf("%d is ", year);
	else
		printf("%d is not ", year);
	printf("a leap year.\n");
	return 0;
}

运行结果

代码优化

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int year, leap;
	printf("Please enter a year:");
	scanf("%d", &year);
	if (year % 4 != 0) leap = 0;
	else if (year % 100 != 0) leap = 1;
	else if (year % 400 != 0)leap = 0;
	else leap = 1;

	if (leap)
		printf("%d is ", year);
	else
		printf("%d is not ", year);
	printf("a leap year.\n");
	return 0;
}

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int year, leap;
	printf("Please enter a year:");
	scanf("%d", &year);
	if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))
		leap = 1;
	else
		leap = 0;
	if (leap)
		printf("%d is ", year);
	else
		printf("%d is not ", year);
	printf("a leap year.\n");
	return 0;
}

例子4.6 运输公司对用户计算运费。运输距离(以s表示,单位为千米)越远,单位运费(以每吨●千米为单位)越低。计算标准如下:

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	int c, s;
	double p, w, d, f;
	printf("请输入单价、重量和距离:");
	scanf("%lf,%lf,%d", &p, &w, &s);
	if (s >= 3000) c = 12;
	else c = s / 250;
	switch (c)
	{
     
	case 0:d = 0; break;
	case 1:d = 2; break;
	case 2:
	case 3:d = 5; break;
	case 4:
	case 5:
	case 6:
	case 7:d = 8; break;
	case 8:
	case 9:
	case 10:
	case 11:d = 10; break;
	case 12:d = 15; break;
	}
	f = p * w * s *(1 - d / 100.0);
	printf("运费:%10.2f元\n",f);
	return 0;
	
}

运行结果

例4.7输入一个字符,判别它是否大写字母， 如果是,将它转换成小写字母;如果不是,不转换。然后输出最后得到的字符。

#define _CRT_SECURE_NO_WARNINGS
#include 
int main()
{
     	
	char ch;
	scanf("%c", &ch);
	ch = (ch >= 'A'&&ch <= 'Z') ? (ch + 32) : ch;
	printf("%c\n", ch);
	return 0;
}

运行结果