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>
#include <math.h>
int main(){
    int i;
    int m,n;
    int count;
    count=0;
    
    for(m=101;m<=200;m++){
    n=sqrt(m);
    for(i=2;i<=n;i++){
        if(m%i==0)break;
    }
    
    if(i>n){
        printf("%6d",m);
        count++;
        if (count%5==0)
        printf("\n");
    }    
    }
    printf("\n101~200间有%d个素数.",count);
    return 0;
}

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

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

int main(int argc, const char * argv[]) {
    int n;
    double s=0,num;
    int x=0,a=1;
    int i;
    double sign=1.0;
    
loop:printf("Enter n(1~10):");
    while(scanf("%d",&n)!=EOF){
        for(i=1;i<=n;i++){
            a=a*i;
            do{
                num=sign/a;
                s=s+num;
                sign=-sign;
                x++;
                continue;
            }while(x<=n);
        }
        printf("n = %d,s = %f\n",n,s);
        s=0;x=0;a=1;sign=1.0;
        goto loop;
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(){
    int n, x, i=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):");
    srand(time(0));
    x= rand()%32;
    scanf("&d",&n);
    while(i<3){
        if(n == x){
            printf("猜中啦！你的luck day是%d号",x);
            break;
        }
        else if(n<x){
            printf("你猜的日期早了，luck day还在后面呢\n");
            i++; 
        }
        else if(n>x){
            printf("你猜的日期晚了，luck day悄悄溜到前面啦\n");
            i++;
        }
        printf("再猜（1~31）；");
        scanf("%d",&n); 
    }
    if(i=3){
        printf("次数用完啦，偷偷告诉你，12月，你的luck day是%d号\n",x);
    } 
    return 0;
}