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 main(){
    int i,m,n,k;
        k=0;
    for(n=101;n<=200;n++)
       {m=sqrt(n);
       for(i=2;;i++)
          {if(n%i==0)break;
          if(i>m&&n>=101){
          printf("%d ",n);
          k++;break;
          }
            }
       }
       printf("101~200之间有%d个素数\n",k);
       return 0;
}

 

 

 

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

m=s%10,算出最低位数字；s=(s-m)/10，将最低位数字减掉；m%2!=0，判断m是否为奇数

m*10^n-1确保丛高位到低位输出

 

 

#include<stdio.h>
#include<math.h>
int main(){
    int i,n,p;
    double s;
    printf("Enter n(1~10)：");
    while(scanf("%d",&n)!=EOF){
        s=1;
        p=1;
        for(i=2;i<=n;i++){
            p=p*i;
            s=s+pow(-1,i-1)*(1.0/p);
        }
        printf("n=%d,s=%lf\n",n,s);
        printf("Enter n(1~10):");
    }
    return 0;
}

 

 

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
    int x,n,i;
    srand(time(NULL));
    x=(int)rand()%31+1;
    printf("猜猜2020年12月那一天是你的luck day\n");
    printf("开始喽，你有三次机会，猜吧（1~31）；");
        for(i=1;i<=3;i++){
            scanf("%d",&n);
            if(n>x)
            printf("你猜的日期晚了，luck day偷偷溜到前面啦\n");
            if(n<x)
            printf("你猜的日期早了，luck day还没到呢\n");
            if(n==x){
            printf("恭喜你，猜对了");
            break;
            }
            if(i<3)
            printf("再猜（1~31）：");
        }
    if(i=4)
    printf("次数用完了，偷偷告诉你：12月，你的luck day是%d号",x);
    return 0;
}