4.2 address calling

• Addressing call is a way to call a function by passing the memory address of the variable created outside the function to the function parameters.
• This parameter transfer method can establish a real relationship between the function and the variables outside the function, that is, the variables outside the function can be directly operated inside the function.

4.3 procedure example 5 Nested calls and chained access to functions

1. Write a function to judge whether a number is a prime number

// Write a function to judge whether a number is a prime number
//is_prime(i)
//Return 1 is a prime
//Returning 0 means it is not a prime number

#include <stdio.h>
#include <math.h>
int is_prime(int n)
{
	//Test with 2~n-1
	//Test with 2~sqrt(n)
	int j = 0;
	for (j = 2; j <= sqrt(n); j++)
	{
		if (n % j == 0)
		{
			return 0;
		}
	}
	return 1;
}
int main()
{
	//Print prime numbers between 100 and 200
	int i = 0;
	for (i = 100; i <= 200; i++)
	{
		//Judge whether i is prime
		if (is_prime(i) == 1)
		{
			printf("%d ", i);
		}
	}
	return 0;
}

2. Write a function to judge whether a year is a leap year

//Write a function to judge whether a year is a leap year
#include <stdio.h>
int is_leap_year(int y)
{
	/*if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0)
		return 1;
	else
		return 0;*/
	return ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0);
}
int main()
{
	//Leap years from 1000 to 2000
	int y = 0;
	for (y = 1000; y <= 2000; y++)
	{
		//Judge whether y is a leap year
		if (is_leap_year(y) == 1)
		{
			printf("%d ", y);
		}
	}
	return 0;
}

3. Write a function to realize the binary search of an integer ordered array

// Write a function to realize the binary search of an integer ordered array
//Return subscript when found
//Return - 1 if not found
#include <stdio.h>
binary_search(int arr[], int k, int sz)
{
	int left = 0;
	int right = sz - 1;
	while (left <= right)
	{
		int mid = left + (right - left) / 2;
		if (arr[mid] < k)
		{
			left = mid + 1;
		}
		else if (arr[mid] > k)
		{
			right = mid - 1;
		}
		else
		{
			return mid;
		}
	}
	return -1;//can't find
}
int main()
{
	//When an array passes parameters, it does not pass the entire array
	//It's the address of the first element passed
	int arr[] = { 1,2,3,4,5,6,7,8,9 };
	int k = 0;
	scanf("%d", &k);//Element to find
	int sz = sizeof(arr) / sizeof(arr[0]);
	int ret=binary_search(arr, k, sz);
	if (-1 == ret)
		printf("can't find\n");
	else
		printf("Yes, the subscript is:%d\n",ret);
	return 0;
}

4. Write a function. Every time this function is called, the value of num will be increased by 1

//Write a function. Every time you call this function, you will increase the value of num by 1
#include <stdio.h>
void test(int* p)
{
	*p = *p + 1;
	//(*p)++;
}
int main()
{
	int num = 0;
	test(&num);
	printf("%d\n", num);
	test(&num);
	printf("%d\n", num);
	test(&num);
	printf("%d\n", num);
	test(&num);
	printf("%d\n", num);
	return 0;
}

5. Nested call and chained access of functions