实验三

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

#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;
}

#include <stdio.h>
int main() {
int n,m,count;
count==0;
for(n=100;n<200;n++) 
{ 
for(m=2;m<=n;m++)
{
if(n%m==0)
{
break;
}
}
if(n==m)
{
count++;
printf("%d ",n);

if(count%5==0)
printf("\n");

}

}
printf("\n这一区间内素数个数:%d\n",count);
return 0 ;
}

#include<stdio.h>
#include<math.h>
int main()
{
int m,n;
printf("Enter a number:");
while(scanf("%d",&n)!=EOF)
{
int i=0,s=0;
do
{
m=n%10;
if(n%2!=0)
{
s=s+m*pow(10,i);
i++;
}
n=n/10;
}while(n!=0);
printf("new number is:%d",s);
printf("\n"); 
printf("Enter a number:");
}
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<time.h>
#include<stdlib.h>
int main()
{
int x,n,i=0;
srand(time(0));
x=1+rand()%31;
printf("猜猜2020年12月哪一天会是你的luck day\n开始喽，你有三次机会，猜吧(1～31):");
while(1)
{
scanf("%d",&n);
if(n==x) 
{
printf("恭喜你猜对了");
break;
}
else
{
if(n>x) 
printf("你猜的日期晚了，luck day悄悄溜到前面啦");
else 
printf("你猜的日期早了，luck day还没到呢");
i=i+1;
if(i>2)
{
printf("\n次数用完了。偷偷告诉你:12月，你的luck day是%d号",x);
break;
}
printf("\n");
printf("再猜(1～31):");
}
}
return 0;
}