练习？

最小公约数
#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main()
{
    int num1 = 0;
    int num2 = 0;
    int r = 0;
    printf("最小公约数");
    scanf("%d%d", &num1, &num2);
    while (num1%num2)
    {
        r = num1%num2;
        num1 = num2;
        num2 = r;
    }
    printf("完毕%d\n",num2);
    return 0;
}

判断闰年
#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main()
{
    int year = 0;
    int count = 0;
    for (year= 1000; year <=2000; year++)
    {
        if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
        {
            printf("  %d年", year);
            count++;
        }
        /*if (year % 4 == 0 && year % 100 != 0)
        {
                printf("  %d年", year);  
                count++;
        }
        else if (year % 400 == 0)
        {
            printf("  %d年", year);
            count++;
        }*/
    }
    printf("\n");
    printf("一共有%d个闰年\n", count);
    return 0;
}

试初法找素数
#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <math.h>

int main()
{
    int i = 0;
    int count = 0;
    for ( i = 100; i <=200; i++)
    {
        int j = 0;
        for (j = 2; j < sqrt(i); j++)
        {
            if (i%j == 0)
            {
                break;
            }
        }
        if (j>sqrt(i))
        {
            count++;
            printf("%d ", i);
        }
    }
    return 0;
}

1~100出现9的次数
#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <math.h>
int main()
{
    int a = 0;
    int i = 0;
    int num1 = 0;
    for ( i = 0; i <= 100; i++)
    {
        if (i%10==9)//i-9%10==0也可以
        {
            num1++;
            printf("%d ", i);
        }
        if(i / 10 == 9)
        {
            num1++;
            printf("%d ", i);
        }
    }
    printf("出现了%d次\n", num1);
    return 0;
}

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <math.h>

int main()
{
    int i = 0;
    double num1 = 0.0;
    int flag = 1;
    for ( i = 1; i <= 100; i++)
    {
        num1 += flag*1.0 / i ;
        flag = -flag;
    }
    printf("%lf\n",num1);
    return 0;
}

9x9乘法表
#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <math.h>

int main()
{
    int i = 0;

    printf("九九乘法表\n");
    for ( i = 1; i <=9; i++)
    {
        int j = 1;
        for ( j = 1; j <=i; j++)
        {
            int max = j*i;

            printf("%d*%d=%-2d ", i, j, max);
        }
        printf("\n");
    }
    return 0;
}