practise函数实现——乘法口诀表，判断素数，交换两数，判断闰年，数组的初始清空逆置

1.实现一个函数，打印乘法口诀表，口诀表的行数和列数自己指定，

    输入9，输出9*9口诀表，输出12，输出12*12的乘法口诀表。 

#include<stdio.h>#include<windows.h> void mutiplycation_form(int num){int i = 0;int j = 0;for (i = 1; i <= num; i++)//确定行数{for (j = 1; j <= i; j++)//确定列数{printf("%d*%d=%d  ", j, i, j*i);}    printf("\n");}}int main(){int num = 0;scanf_s("%d", &num);mutiplycation_form(num);system("pause");return 0;}

2.使用函数实现两个数的交换。 

#include<stdio.h>#include<windows.h>void swap(int *x, int *y){int temp = *x;*x = *y;*y = temp;}int main(){int a = 10;int b = 20;swap(&a, &b);//地址传递printf("%d  %d", a, b);system("pause");return 0;}
3.实现一个函数判断year是不是闰年。
#include<stdio.h>#include<windows.h>int is_leap(int n)//是闰年返回1，不是返回0{   if (n % 400 == 0 || (n % 4 == 0 && n % 100 != 0))return 1;else        return 0;}int main(){int year=0;scanf_s("%d", &year);if(is_leap(year)){printf("%d is leap year\n",year);}else printf("%d is not leap year\n", year);system("pause");return 0;}
4.实现一个函数，判断一个数是不是素数。
#include<stdio.h>#include<windows.h>int is_prime(int n){int i = 0;for (i = 2; i < n; i++){if (n%i == 0)    return 0;}return 1;}int main(){int num = 0;scanf_s("%d", &num);if(is_prime(num))    printf("%d is prime\n",num);else printf("%d is not prime\n", num);system("pause");return 0;}
5.创建一个数组， 实现函数init（）初始化数组、 empty（）清空数组、 reverse（）函数完成数组元素的逆置。
要设计函数的参数，返回值。 
#include<stdio.h>#include<windows.h>void init(int arr[],int len,int set){printf("初始化数组：\n");int i = 0;for (i = 0; i < len; i++){arr[i] = set;}}void empty(int arr[], int len){printf("清空数组：\n");int i = 0;for (i = 0; i < len; i++){arr[i] = 0;}}void reverse(int arr[],int len){printf("逆置数组：\n");int left = 0;int right = len - 1;int temp = 0;     while(left < right){temp = arr[left];arr[left] = arr[right];arr[right]= temp;left++;right--;}}void print(int arr[], int len){int i = 0;for (i = 0; i < len; i++)printf("%d ", arr[i]);printf("\n");}int main(){int arr[10] = {1,2,3,4,5,6,7,8,9,10 };int len = sizeof(arr) / sizeof(arr[0]);init(arr, len,3);print(arr,len);empty(arr, len);print(arr, len);reverse(arr, len);print(arr, len);system("pause");return 0;}