实验3

一

#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;
    
}

 

 

二

#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;
}

 

 

三

#include<stdio.h>
int main(){
    
    int x;
    int sum;
    sum =0;

    for( x=100; x<=200; x++ ){
        int i;
        int isPrime = 1; //x是素数 
        for ( i=2; i<x; i++ ) {
            if ( x % i == 0 ) {
            
                isPrime=0;
                break;
            }
            
        }
        if ( isPrime == 1 ) {
            
            printf("%d ",x );
            sum++;
            if(sum%5==0) printf("\n"); 
        }
    }
    printf("\n");
    printf("101~200之间素数有%d个",sum);
    return 0;
} 

 

 

四

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

 

 

1.%2！=0

2.f*10

 

五

#include<stdio.h>
int main(){
    int n,m;
    double s,x;
    printf("Enter n(1~10):");
    while(scanf("%d",&n)!=EOF){
        s=0;
    for(;n>0;n--){
        x=1;
        for(m=n;0<m;m--){
        x=x*m;
     }
        if(n%2==0)
        s = s - 1.0 / x;
        else 
        s = s + 1.0 / x;
    }
    printf("n=%d, s=%f",n, s);
}

    return 0;
    
    
}

 

 

六

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(){
    int x, n,a;
        
    srand(time(0));
    n = 0;
        x = rand()%31+1;
        printf("猜猜2020年12月会是你的luck day\n");
        printf("开始了，你有三次机会，猜吧\n");
    
    for(n=3;n>0;n--){
        
    scanf("%d",&a);
    if(a==x){
    
    printf("yes\n");

    break;
}
    else if(a<x)
    printf("小了\n");
    else if(a>x)
    printf("大了\n");
        
    }
    printf("the day is %d\n",x);
    
    return 0;
}