实验三

#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>
#include <math.h>
int isPrime();
int isPrime(){
	int i,m,n,p=0;
	for(n=101;n<201;n++){
		m=sqrt(n);
		for(i=2;i<=m;i++)
			if(n%i==0)break;
		if(i>m&&n>1){
			printf("%6d",n);
			p++;
			if(p%5==0)
				printf("\n");
		}
	}
	return p;
}
int main(){
	int a;
	a=isPrime();
	printf("\n100~200之间有%d个素数。",a);
	return 0;
}

　　

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

    return 0;
}

　　

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

int main()
{
    int n, i, factorial = 1;
    double s = 0, sign = 1.00000;
    
    printf("enter n(1~10):");
    
    while(scanf("%d",&n) != EOF)
    {
    
        for(i=1;i<=n;i++)
        {
            factorial = factorial * i;
            sign = pow(-1,i+1);
            s = s + sign/factorial;
            continue;
        }
        
        printf("n = %d  s = %f\n", n, s);
        
        s = 0;
        factorial = 1;
        sign = 1.00000;
        
        printf("enter n(1~10):");
    }
      return 0;
}

　　

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
    int a,x,n;    
    srand(time(0));
    x=rand()%31+1;
    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)：");
    scanf("%d",&a);
    for(n=1;n<=3;n++){
        if(n!=3){
        if(a>x){
        printf("\n你猜的日期晚了，luck day悄悄溜到前面啦\n");
        printf("再猜（1~31）：");                
        }
        if(a<x){
        printf("\n你猜的日期早了，luck day还没到呢\n");
        printf("再猜（1~31）：");                
        }
        scanf("%d",&a);
        
        }        
        if(a==x)
        break;
        if((n==3)&&(a!=x))
        printf("\n\n次数用完啦。偷偷告诉你：12月，你的luck day是%d号",x);        
    }
    return 0;
}