实验三

实验任务一
#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;
}

实验任务二

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

int main() {
    int x, n ,i; 
    
    srand(time(0)); 
    x = rand() % 31+1; 

    
    printf("猜猜2021年5月哪一天会是你的lucky day\n开始咯，你有三次机会，猜吧（1^31）:",x);
    for(i=1;i<=3;i++){
        scanf("%d",&n);
        if(n==x){
            printf("你猜对了，%d日就是你的lucky day",x);
            break;
        }
        else if(n<x){
            if(i<=2)
            printf("你猜的日期早了，lucky day还没到呢\n再猜：");
            
            else 
            printf("次数用完了，偷偷告诉你：你的lucky day是%d日",x);
        }
        else if(n>x){
            if (i<=2)
            printf("你猜的日期晚了，lucky day悄悄溜到前面了\n再猜：");
            else
            printf("次数用完了，偷偷告诉你：你的lucky day是%d日",x);
        }
        
    }
    
    return 0;
} 

实验任务三

#include<stdio.h>
int main (){
    long s;
    printf("enter a number:");
    while((scanf("%ld",&s))!=EOF){
        long t=0,p=1;
        while(s!=0)
        {
            if((s%10)%2!=0)
            {
                t=t+(s%10)*p;
                p=p*10;
            }
            s=s/10;
        }
        printf("new number is:%ld\n",t);
        printf("enter a number:");
    }
    return 0;
}

实验任务四

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

思考：否，函数值只能返回一个，无法返回x1,x2两个值。

实验任务五

#include<stdio.h>
double fun(int n);

int main(){
    int n;
    double s;

    while(printf("Enter n(1~10):"),scanf("%d", &n) != EOF){
        s = fun(n);
        printf("n = %d, s = %f\n\n", n, s);
    }

    return 0;
}

double fun (int n){
    int i,z,a=1,d=1;
    double b,s;
    for(i=1,s=0;i<=n;i++,a=1)
    {
    for(z=i;z>0;--z){
        a=a*z;
    }    
        b=d*1.0/a; 
        s=s+b;
        d=-d;
    }
    return s;
}

实验任务六

#include<stdio.h>
#include<math.h>
int isprime(int n);
int main(){
    int i,n;
    for(i=101,n=1;i<=200;i++)
    {
        if(isprime(i)){
    
           printf("%4d",i);
           n++;
        }
        if(n%6==0){
           printf("\n");
           n=1;}
    }
    return 0;
}
int isprime(int n)
{
    int k;
    for(k=2;k<=sqrt(n);k++)
       if(n%k==0)
          return 0;
       return 1;
}

实验总结：能感觉到难度明显加大，花费的时间是之前的几倍，路漫漫其修远兮，干巴爹。。。