c语言学习笔记（6）——for和while循环

for和while等价替换

--------------------------

int i = 1;

for (i; i<=100; i++){

sum = sum + 1;

}

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int i = 1;

while(i<=100){

sum = sum + 1;

i++;

}

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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\n");

}else{

printf("no\n");

}



return 0;

}

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斐波拉器序列：

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：\n");

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\n", f3);

return 0;

}

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do....while....实现一元二次方程

do....while....至少执行一次

# 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:\n");

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\n", x1, x2);

}

else if (0 == delta)

{

x1 = x2 = (-b) / (2*a);

printf("有唯一解，x1 = x2 = %lf\n", x1, x2);

}

else

{

printf("无实数解!\n");

}





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;

}

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