Function call:

1. The call-by-
function parameter arguments and occupy different memory blocks, respectively, of the modification of the parameter does not affect the argument.
2. call pass-
pass-calling is the way to pass the memory address of the function of external variables to create a way to call the function arguments.
This approach allows parameter passing variables outside of functions and function is really to establish a positive relationship, that is, the internal function can be directly manipulated variables outside the function.

Exercise:
1. Call function to achieve two-digit exchange

#include <stdio.h>
int Swap(int *pa, int *pb)    
{
	int temp = 0;
	temp = *pa; //等价于temp=a;
	*pa = *pb;
	*pb = temp;
	return 0;
}
int main()
{
	int a = 10;
	int b = 20;
	printf("a=%d b=%d\n", a, b);
	Swap(&a, &b);
	printf("a=%d b=%d\n", a, b);

	return 0;
}.

2. Call function to identify a leap year between 1000-2000

int is_leap_year(int y)                       //调用函数找出润年
{
	
	if ((y % 4 == 0 && y % 100 != 0) || (y % 400 == 0))
	{
		return 1;
	}
	else
	{
		return 0;
	}
}
int main()
{
	int count = 0;
	int year = 0;
	for (year = 1000; year < 2001; year++)
	{
		if (is_leap_year(year) == 1)
		{   
			count++;
			printf("%d ", year);
			
		}
	}
	printf("count=%d\n", count);
	return 0;
}

3. Call function to find prime numbers between 100-200

#include <math.h>  //sqrt引用的头文件
int is_prime(int n)
{
	//判断n是否为素数
	int i = 0;
	for (i = 2; i < sqrt(n); i++)
	{
		if (n%i == 0)
		{
			return 0;
		}
	}
	return 1;
}

int main()
{
	int count = 0;
	int i = 0;
	for (i = 100; i <= 200; i++)
	{
		if (is_prime(i) == 1)
		{
			printf("%d\n", i);
			count++;
		}
	}
	printf("%d\n", count);
	return 0;
}

4. Call function using a binary search to find the specified element subscript

int binary_search(int arr[], int k,int sz)
{
	int left = 0;
	int right = sz - 1;
	int mid = (left + right) / 2;
	while (left <= right)
	{
		if (arr[mid] < k)
		{
			left = mid + 1;
		}
		else if (arr[mid]>k)
		{
			right = mid - 1;
		}
		else
		{
			return mid;
		}
	 }
	return -1;

}
int main()
{
	int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	int k = 0;
	int sz = sizeof(arr) / sizeof(arr[0]);

	scanf("%d", &k);
	//数组传参的时候，传过去一个数组名，本质上传过去的是数组首元素的地址
    int ret=binary_search(arr,k,sz);      //二分查找     找到返回下标，找不到返回-1
	if (ret == -1)
	{
		printf("找不到\n");
	}
	else
	{
		printf("找到了，下标是%d\n", ret);
	}
	return 0;
}