实验三

#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 <stdlib.h>
#include <time.h>
int main() {
    int x,y,i; 
    printf("猜猜2021年5月哪一天会是你的luck day\n\n");
    srand(time(0)); 
    x = rand() % 31; 
    x++;
    printf("开始喽，你有三次机会，猜吧（1~31）:");

    for(i=1;i<=3;i++){
        if(i>1){
            printf("\n");
            printf("再猜(1~31):");
        }
        scanf("%d",&y);
        printf("\n");
        if(y>x){
            printf("\n");
            printf("你猜的日期晚了，luck day悄悄溜到前面啦\n"); 
        } 
        else if(y<x){
            printf("\n");
            printf("你猜的日期早了,luck day还没到呢\n");
        }
        else if(y=x){
            printf("\n");
            printf("你猜中了\n");
            return 0;
        }    
    }
    printf("\n");
    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>
#include <math.h>
int main(){
    long s;
    int n,x,i;
    while(printf("Enter a number:"),scanf("%ld",&s)!=EOF){
        x=0;
        i=0;
        while(s!=0){
            n=s%10;
            s=s/10;
            if(n%2!=0){
               x=x+n*pow(10,i);
               i++;
            }
        }
        printf("new number is:%d\n\n",x);
    }
    return 0;
}

#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);
        }
    }    
}

#include <stdio.h>
#include <math.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) {
    int m,i,j;
    double s;
    s=0;
    for(i=1;i<=n;i++){
        m=1;
        for(j=1;j<=i;j++){
            m=m*j;
        }
        s=s+pow(-1,i-1)*(1.0/m);        
    }
    return s;
}

#include <stdio.h>
#include<math.h>
int isPrime(int x);
int main (){
    int n,t;
    t=0;
    for(n=100;n<=200;n++){
        if(isPrime(n)){
            t++;
            printf("%4d",n);
            if(t%5==0){
                printf("\n");
            }                        
        }
    }
    printf("\n\n");
    printf("100~200之间素数个数为:%d",t);    
}

int isPrime(int x){
    int k;
    for(k=2;k<=sqrt(x);k++){
        if(x%k==0){
            return 0;
        }
    }
    return 1;    
}