实验3

#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%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,i,k=0;
    for(n=101;n<=200;n++){
        int j=0;
        for(i=2;i<=n;i++)
        if(n%i==0)
        {
          j++;
        }
        if(j==1)
        {
            printf("%d\n",n);
            k++;
        }
        
    
    }
    printf("101~200之间一共有%d个素数",k); 
    
    
    
    return 0;
} 

#include<stdio.h>
int main(){

long int s,t,m=0,n=1;
scanf("%ld",&s);
printf("Enter a number is:%ld\n",s);
while(s){
     t=s%10;
     if(t%2!=0)
     {
         m=m+t*n;
         n=n*10;
         }    
         s=s/10;
    
}
printf("new number is:%ld\n",m);
return 0;
}

#include<stdio.h>
#include<stdlib.h>
int main(){
    double sum=0,p=1;
    int n,i;
    
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        p=p/i;
        if(i%2==0)
        {sum=sum-p;
        }
        else{sum=sum+p;
        }
    }
    printf("n=%d,sum=%lf",n,sum);
    
    
    
    return 0;
} 

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

int main(){
    int m,n,t;
    srand((int)time(0)) ;
    t=rand()%30;
    n=1;
    printf("2020which day is lucky day?\n");
    scanf("%d",&m);
    while(n<=2){
        if(m<t){
            printf("It is too early\ntry again");
            scanf("%d",&m);
            n++;
        }
        else if(m>t){
            printf("It is too late\ntry again");
            scanf("%d",&m);
            n++;}
            else if(m=t){
                printf("Got it!");
                n++;
            }
            
        }
        printf("To tell you,in December,your lucky day is:%d",t);
    return 0;}