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",&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 x,count;
    x=101;
    count=0;
    for(x=101;x<=200;x++){
    int i;
    int t=1;
    for(i=2;i<x;i++){
    if(x % i == 0){
    t=0;
    break;
    }
    }
    if(t==1){
    count++;
    printf("%5d",x);
    if(count%5==0){
    printf("\n");
    }
    } 
    }
    printf("\n101~200之间共有%d个素数.",count);
    
    return 0;
}

#include<stdio.h>
int main(){
    int x,i,t,r;
    int ret=0;
    i=0;
    
    printf("Enter a number is:");
    
    while(scanf("%d",&x)!=EOF){
    while(x>0)
    {
        t=x%10;
        x=x/10;
        if(t%2>0){
            i=i*10+t;
        }
    }
    while(i>0){
        r=i%10;
        i/=10;
        ret=ret*10+r;
    }
    printf("new number is:%d\n",ret);
    ret=0;
    printf("\nEnter a number is:");
    }
    return 0;
}

先分解数据，然后用2判断奇偶性，最后排列输出。

#include<stdio.h> 
#include<math.h>
int main(){ 
    int n,i;
    printf("Enter n(1~10):");
    while(scanf("%d",&n)!=EOF){
        int n1=n;
        double s=0;
        while(n1>0){
            double x=1;
            for(i=1;i<=n1;i++){
                x=x*i;
            }
                s=s+pow(-1,n1-1)*1/x;
                n1--;
            }
            printf("n=%d,s=%lf\n",n,s);
            printf("\nEnter n(1~10):");
        }
        return 0; 
    }

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

int main(){
    srand(time(0));
    int number = rand()%31+1;
    int count = 0;
    int a;
    
    printf("猜猜2020年12月哪一天会是你的luck day\n");
    printf("开始喽，你有三次机会，猜吧（1~31）：\n"); 
    while(count<3){
        scanf("%d",&a);
        if(a>number){
            printf("你猜的日期晚了，luck day悄悄溜到前面啦\n"); 
        }
        else if(a<number){
            printf("你猜的日期早了，luck day还没到呢\n");
        }
        else if(a=number){
            printf("猜对啦，你的luck day的确是这一天)");
            return 0;
        }
        count++;
        if(count<3){
            printf("再猜(1~31)\n");
        }
    }
    printf("\n次数用完啦。偷偷告诉你：12月，你的luck day是%d号",number);
    return 0;
}