Functions in C language

Let's give you an example

#include<stdio.h>

void print_C();  // Declaration of functions , Statement statement , There's a semicolon behind it 

void print_C()   // Definition of function 
{
	printf(" ###### \n");
    printf("##    ##\n");       
	printf("##      \n");
	printf("##      \n");
	printf("##      \n");
	printf("##    ##\n");
	printf(" ###### \n");
}

int main()
{
	print_C();   // Function call 
	printf("\n");
	print_C();
	printf("\n");
	print_C();

	return 0;
}

One 、 Definition of function ：
        Type name   Function name （ parameter list ） It is usually named with the corresponding function
       ( The return value of the function , If you do not need to return, use void) 
       {
                The body of the function
       }

Two 、 Declaration of functions
      The so-called declaration （Declaration), Just tell the compiler that I want to use this function , It doesn't matter that you haven't found its definition now , Please don't make mistakes , I'll fill in the definition later .

As in the above example , If you don't write a function declaration , The compiler may report errors

3、 ... and 、 Parameters and return values of functions
    eg：1、 Write a function sum, Input parameters by the user n, Calculation 1+2+3+....+（n-1）+n And return .

#include<stdio.h>

int sum(int n);

int  sum(int n)  // Formal parameters , Define a function sum
{
	int result = 0;
	do
	{
		result += n;
	} while (n-- > 0);
	return result;
}

int main()
{
	int n, result;
	printf("input the value of n:\n");
	scanf("%d", &n);

	result = sum(n);  // The actual parameter 

	printf("1+2+3+4+...+(n-1)+n The result is ：%d\n", sum(n));

	return 0;
}

  2、 Write a function max, Receive two integer parameters , And return the larger of them .

#include<stdio.h>

int max(int, int);   // You don't have to define , Just state the type 

int max(int x, int y)  // Must be defined x,y
{
	if (x > y)
		return x;   // If x>y, return x Value 
	else
		return y;
}

int main()
{
	int a, b, c;
	printf(" Please enter two integers ：");
	scanf("%d,%d", &a, &b);

	c=max(a, b);
	printf(" The larger of them is ：%d\n", c);
	return 0;
}