#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main() {
    int n = 1, x, b;
    srand(time(0));
    b = rand() % 31 + 1;
    printf("猜猜2020哪一天是你的luck day\n");
    printf("開始嘍，你有三次機會，猜吧（1~31）：");
    scanf_s("%d", &x);
            while(n<3) {
                if (x == b) {
                    printf(
 
"猜中了"); break;
                }
                else if(x<b)
                    printf("早\n");
                else
                    printf("晚\n");
                printf("再猜：");
                scanf_s("%d", &x);
                n++;    
            }
            if(n=3)
            printf(
 
"次數用完了，告訴你吧，12月，你的luck day是%d", b);
        return 0;
    }

#include<stdio.h>
#include<math.h>
#define EOF -1
int main() {
    int  n;
    double a,b=1,s = 0.0,k=1;
    printf("Enter n(1~10):");
    while (scanf_s("%d", &n) != EOF) {
        if (n >= 1 && n <= 10) {
        

            
 
for (; k <= n;) {
                
                b = b * k;
                a = pow(EOF, k - 1.0);
                s = s +a * (1 / b);
                k++;
            
            }
            printf("n=%d,s=%f\n", n, s);
            printf("Enter n(1~10):");
        }
    }
    return 0;
}

#include<stdio.h>
#include<math.h>
int main() {
    float a, b, c, x1, x2;
    float delta, real, imag;
    printf("Enter a,b,c:");
    while (scanf_s("%f%f%f", &a, &b, &c) != EOF) {
        if (a == 0)
            printf("not quadratic equation.\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", x1, x2);
            }
            else {
                real = -b / (2 * a);
                imag = sqrt(-delta) / (2 * a);
                printf("x1 = %.2f + %.2fi, x2 = %.2f - %.2fi\n", real,
                    imag, real, imag);
            }
        }
        printf("Enter a, b, c: ");
    }
    return 0;

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    int k,i=101, j, m;
    m = 0;
    while(i<=200)
    {
        j=sqrt(i);
        for (k = 2; k <= j; k++)
            if (i % k == 0)break;
            if (k > j)
        {
            printf("%d\t", i);
            m++;
        }
        i++;
    }
    printf("101~200之間有%d個素數", m);
}

#include<stdio.h>
#include<math.h>
int main() {
    int n, a, b, i, sum;
    printf("請輸入一個長整型變數：");
        scanf_s("%d", &n);
    i = 0;
    sum = 0;
    while (n != 0)
    {
        a = n % 10;
        b = a % 2;
        if (b != 0) {
            sum = sum + a * pow(10, i);
                i++;
        }
        n /= 10;
    }
    printf("%d", sum);
    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;

}