实验3

`#include<stdio.h>

include<math.h>

int main(){
float a,b,c,x1,x2;
float delta,real,imag;

printf("Enter a,b,c:  ");

while(scanf("%f%f%f",&a,&b,&c)!=EOF){
    if(a==0)
        printf("not quadratic equation.\n\n");
    else{
        delta = b*b-4*a*c;
        
        if(delta>=0){
            x1 = ((-b+sqrt(delta))/(2*a));
            x2 = ((-b-sqrt(delta))/(2*a));
            printf("x1=%.2f,x2=%.2f\n\n",x1,x2); 
        }
        else{
            real = -b/(2*a);
            imag = sqrt(-delta)/(2*a);
            printf("x1 = %.2f+%.2fi,x2 = %.2f - %.2fi\n\n",real,imag,real,imag);
        }
    }
    
    printf("Enter a,b,c: ");
}

return 0;

} `

`//生成N个0~9之间的随机整数，并打印输出

include<stdio.h>

include<stdlib.h>

include<time.h>

define N 5

int main(){
int x,n;
srand(time(0));
n=0;
do{
n++;
x = rand()%10;
printf("%3d",x);
}while(n<N);
printf("\n");
return 0;
}![](https://img2020.cnblogs.com/blog/2184252/202011/2184252-20201123185547279-1026336281.png)#include<stdio.h>

include<math.h>

include<stdlib.h>

int main(){ int a,i,n,m;
for(n=101,a=0;n<=200;n++){
m=sqrt(n);
for(i=2;i<=m;i++)
if(n%i0)break;
if(i>m){
printf("%5d",n);
a++;if(a%50)printf("\n");
}
//else
//continue;
}
printf("\n101~200之间共有%d个素数",a);
return 0;
}`

`#include <stdio.h>

include <stdlib.h>

int main()
{ int a,c;
long s,xin;
printf("enter a number:");

while(scanf("%ld",&s)!=EOF)
{  
     
    xin=0;
    c=1;
    while(s>0)
    {  
         
        a=s%10;
        s=s/10;
        if(a%2!=0)
        {
            xin=xin+c*a;
            c=c*10;
        }
    }
    if (xin==0)
        printf("输入数据中不含奇数\n");
    else    
        printf("new number is:%ld\n",xin);
     
    printf("enter a number:");
}
 
system("pause");
return 0;       

}`

`#include<stdio.h>

include<math.h>

include<stdlib.h>

int main(){
float s,sum;
int n;

printf("Enter n(1~10):");
    
while(scanf("%d",&n)!=EOF){
    
    sum=0.0,s=1.0;
    int i;
    
for(i=1;i<=n;++i){
    s=s*i;
    sum=sum+pow(-1,i-1.0)/s;
}
printf("n=%d,sum=%lf\n",n,sum);
printf("Enter n(1~10):\n");}
return 0;

}
`

`#include<stdio.h>

include<stdlib.h>

include<time.h>

int main(){
int x,answer,i;

srand(time(0));
x= rand()%31+1;

printf("猜猜2020年12月哪一天会是你的Luck day");
printf("开始喽，你有三次机会，猜吧（1~31）：");
for (i=1;i<=3;i++)
{
scanf("%d",&answer);
if(answer>x)
printf("你猜的日期晚了，luck day悄悄溜到前面了");
else if(answer<x)
printf("你猜的日期早了，luck day 还没来呢");
else
break;
}

if(i==3)
printf("次数用完了,你的luck day 是%d",x);

return 0;

}`