自定义函数

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。

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int Mul(int m){
	for (int line = 1; line <= m; ++line){
		for (int column = 1; column <= line; ++column){
			int ret = line * column;
			printf("%d*%d=%2d\t", line, column, m);
		}
		printf("\n");
	}
}
int main(){
	int num = 0;
	printf("input a number:");
	scanf("%d",&num);
	Mul(num);
	system("pause");
	return 0;
}

使用函数实现两个数的交换（指针）

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>
void Swap(int* x, int* y){
	int tmp = *x;
	*x = *y;
	*y = tmp;
}
int main(){
	int i = 10;
	int j = 20;
	Swap(&i, &j);
	printf("i=%d\n", i);
	printf("j=%d\n", j);
	system("pause");
	return 0;
}

实现一个函数判断year是不是润年。

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int Isleap(int i){
	if (i % 100 != 0){
		if (i % 4 == 0){
			return 1;
		}
		printf("\n");
		return 0;
	}
	if (i % 400 == 0){
		return 1;
	}
	return 0;
}
int main(){
	int ret = 0;
	int year = 0;
	printf("input a number:");
	scanf("%d", &year);
	ret = Isleap(year);
	if (ret == 1){
		printf("it is a leap year");
	}
	else{
		printf("it is not a leap year");
	}
	system("pause");
	return 0;
}

实现一个函数，判断一个数是不是素数。

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>
int Isprime(int i){
	if (i == 1){
		return 0;
	}
	for (int j = 2; j <sqrt(i); j++){
		if (i%j == 0){
			return 0;
		}
	}
	return 1;
}
int main(){
	int num = 0;
	int ret = 0;
	printf("please input a number:\n");
	scanf("%d", &num);
	ret=Isprime(num);
	if (ret == 1){
		printf("is a prime number");
	}
	else{
		printf("is not a prime number");
	}
	system("pause");
	return 0;
}