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 ");
}else{
printf("no ");
}

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： ");
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;
}
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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: ");
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;
}
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