For declaring and defining functions in C++ we have the syntax and we have to follow it.

The general form for declaring a function in C++ is:

/* Signature of function */

return_type function_name( parameter list )
{
   body of the function
}

• Return Type: The return type specifies what a function should return.

• Function Name: This is the name by which we call and access it.

• Parameters: Parameters are used to find values and results at runtime.

• Function Body: It is the collection of the logic that the function performs.

// function returning the max between two numbers
 
int max(int num1, int num2) 
{
   // local variable declaration
   int result;
 
   if (num1 > num2)
      result = num1;
   else
      result = num2;
 
   return result; 
}

Types of arguments passed into the function:

#include <iostream>
using namespace std;
 
int sum(int a, int b=20)
{
  int result;

  result = a + b;
  
  return (result);
}

int main ()
{
   // local variable declaration:
   int a = 100;
   int b = 200;
   int result;
 
   // calling a function to add the values.
   result = sum(a, b);
   cout << "Total value is :" << result << endl;

   // calling a function again as follows.
   result = sum(a);
   cout << "Total value is :" << result << endl;
 
   return 0;
}