忙里偷闲( ˇˍˇ )闲里偷学【C语言篇】——（4）for == while ?

一、for和while等价替换

int i = 1;
for (i; i<=100; i++){
	sum = sum + 1;
}

int i = 1;
while(i<=100){
	sum = sum + 1;
	i++;
}

二、从键盘输入一个数字，如果该数字是回文数，则返回yes,否则返回no

回文数：正着写倒着写一样的数

# include<stdio.h>

int main(){
	int val, m, sum=0;
	printf("请输入您需要判断的数字：");
	scanf("%d", &val);
	
	m = val;
	while(m){
		sum = sum * 10 + m%10;
		m /= 10;
	}
	if(sum==val){
		printf("yes
");
	}else{
		printf("no
");
	}
	
	return 0;
}

三、斐波拉契数列

1 2 3 5 8 13 21 34.....
从第三项开始每一项是前两项的和

# include <stdio.h>

int main(void){
	int n;
	int f1, f2, f3;
	int i;

	f1 = 1;
	f2 = 2;
	
	printf("请输入您需要求得项的序列：
");
	scanf("%d", &n);

	if(1==n){
		f3 = 1;
	}else if(2==n){
		f3 = 2;
	}else{
		for(i=3; i<=n; i++){
			f3 = f1 + f2;
			f1 = f2;
			f2 = f3;
		}
	}
	printf("%d
", f3);
	return 0;
}

四、do....while....实现一元二次方程

# include <stdio.h>
# include <math.h>

int main(void)
{
	double a, b, c;	
	double delta;
	double x1, x2;	
	char ch;
	
	do	
	{	
		printf("请输入一元二次方程的三个系数:
");
		printf("a = ");
		scanf("%lf", &a);
		
		printf("b = ");
		scanf("%lf", &b);
		
		printf("c = ");
		scanf("%lf", &c);
		
		delta = b*b - 4*a*c;
		
		if (delta > 0)
		{
			x1 = (-b + sqrt(delta)) / (2*a);
			x2 = (-b - sqrt(delta)) / (2*a);
			printf("有两个解，x1 = %lf, x2 = %lf
", x1, x2);
		}
		else if (0 == delta)
		{
			x1 = x2 = (-b) / (2*a);
			printf("有唯一解，x1 = x2 = %lf
", x1, x2);
		}
		else
		{
			printf("无实数解!
");
		}

		printf("您想继续么(Y/N): ");
		scanf(" %c", &ch);  //%c前面必须得加一个空格 原因略
	} while ('y'==ch || 'Y'==ch);
	
	return 0;
}