实验3

#include<stdio.h>
#include<stdlib.h> 
#include <time.h>
#define N 5
int main(){
    int x, n;
    
    srand(time(0));
    
    for(n=1;n<=N;n++){
    x = rand() % 100; 
    printf("%3d", x);
    
    }
    printf("\n");
    
    return 0;
}

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

void solve(double a, double b, double c);

int main(){
    double a, b, c; 
    printf("Enter a, b, c: "); 
    while(scanf("%lf%lf%lf", &a, &b, &c) != EOF){
    solve(a, b, c); 
    printf("Enter a, b, c: ");
    }
    
    return 0;
}

void solve(double a, double b, double c){
    double x1, x2; 
    double delta, real, imag; 
    
    if(a == 0) 
    printf("not quadratic equation.\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", x1, x2); 
    
    }    
    else{
    real = -b/(2*a);
    imag = sqrt(-delta) / (2*a); 
    printf("x1 = %.2f + %.2fi, x2 = %.2f - %.2fi\n", real, imag, real, imag);     
    }    
        
        
    }
    
}

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 3

int main() {
    int x, n, i; 
    printf("猜猜2021年5月哪一天会是你的 Lucky Day\n开始喽，你有三次机会，猜吧（1~31）：");
    srand(time(0)); 
    x =1+ rand() % 31; 
    
    for (i=1;i<=3;){
    
        scanf("%d",&n);
        if (n==x){
        printf("猜对啦！\n");
        break;
            
            }
        
        else if (n<x){
        printf("你猜的日期早了，Luck Day还没到呢。\n");
                
            }
                         
        else {
            
        printf("你猜的日期晚了，Luck Day悄悄溜到前面啦。\n"); 
                
            }
            
        i++;    
        printf("再猜(1~31)：");    
            
    if (i>3)
        printf("次数用完啦，偷偷告诉你：5月，你的Luck Day是%d号。\n",x);
               
    }
        
    return 0;
}

#include <stdio.h> 
double fun(int n); 
int main() {
    int n;
    double s;
    
    printf("Enter n(1~10): ");
    while(scanf("%d", &n) != EOF) { 
    s = fun(n); 
    printf("n = %d, s= %f\n\n", n, s); 
    printf("Enter n(1~10): ");
  }
   return 0;
} 



    double fun(int n){
    double one=1,ans=0,i;
    for(i=1;i<=n;i++){
    ans=ans+one;
    one=(-1)*one*(1/(i+1));
        }
        
    return ans;
        
    }

#include<stdio.h>
#include<math.h>
int main(){
    int k,num=0;
    for(k=101;k<=200;k++)
    {
        int i;
        for(i=2;i<=sqrt(k);i++)
        if(k%i==0)
        break;
        if(i>sqrt(k))
        {
        printf("%d ",k);
        num++;
        if(num%5==0)
        printf("\n");
        }
    }
    printf("\n100~200之间素数个数为：%d",num);
    return 0;
}