C++ Tutorial/Function/function definition

Compare pass-by-value and pass-by-reference with references

<source lang="cpp">#include <iostream> using std::cout; using std::endl; int byValue( int ); void byReference( int & );

int main() {

  int x = 2; 
  int z = 4; 
  cout << byValue( x ) << endl;  
  cout << "x = " << x << endl;
  byReference( z );
  cout << "z = " << z << endl;
  return 0;

} int byValue( int number ) {

  return number *= number;

} void byReference( int &numberRef ) {

  numberRef *= numberRef; 

}</source>

4
x = 2
z = 16

Default arguments with parameters

<source lang="cpp">#include <iostream> using std::cout; using std::endl; int f( int length = 1, int width = 1, int height = 1 ); int main() {

  cout << f();
  
  cout << f( 10 );
       
  cout << f( 10, 5 );
  
  cout << f( 10, 5, 2 ) << endl;
  return 0;

} int f( int length, int width, int height ) {

  return length * width * height;

}</source>

11050100

Define function to add two parameters together

<source lang="cpp">#include <iostream>

int Add (int x, int y)
{
    std::cout << "In Add(), received " << x << " and " << y << "\n";
    return (x+y);
}

int main()
{
    std::cout << "The value returned is: " << Add(3,4);
    return 0;
}</source>

In Add(), received 3 and 4
The value returned is: 7

Definition of function template maximum

<source lang="cpp">#include <iostream> using std::cout; using std::cin; using std::endl;

template < class T > T maximum( T value1, T value2, T value3 ) {

  T maximumValue = value1; 
  if ( value2 > maximumValue )
     maximumValue = value2;
  if ( value3 > maximumValue )
     maximumValue = value3;
  return maximumValue;

}

int main() {

  int int1, int2, int3;
  int1 = 1;
  int2 = 2;
  int3 = 3;
  cout << "\nThe maximum integer value is: " << maximum( int1, int2, int3 );
     
  double double1, double2, double3;
  double1 = 1.1;
  double2 = 2.2;
  double3 = 3.3;
  cout << "\nThe maximum double value is: "<< maximum( double1, double2, double3 );
  char char1, char2, char3;
  char1 = "a";
  char2 = "b";
  char3 = "c";
  cout << "\nThe maximum character value is: "<< maximum( char1, char2, char3) << endl;
  return 0;

}</source>

The maximum integer value is: 3
The maximum double value is: 3.3
The maximum character value is: c

Functions in an expression: order of evaluation

<source lang="cpp">#include <iostream>

1. include <ostream>

using namespace std; int x = 1; int f() {

 x = 2;
 std::cout << "f()";
 return x;

} int g() {

 std::cout << "g()";
 return x;

} int main() {

 std::cout << f() / g() << "\n";

}</source>

f()g()1

Functions that take no arguments.

<source lang="cpp">#include <iostream> using std::cout; using std::endl; void f1(); void f2( void ); int main() {

  f1(); 
  f2(); 
  return 0; 

} void f1() {

  cout << "f1 takes no arguments" << endl;

} void f2( void ) {

  cout << "f2 also takes no arguments" << endl;

}</source>

f1 takes no arguments
f2 also takes no arguments

The function call stack and activation records

<source lang="cpp">#include <iostream> using std::cin; using std::cout; using std::endl; int f( int ); int main() {

  int a = 10; 
  cout << a << " fd: " << f( a ) << endl;
  return 0;

} int f( int x ) {

  return x * x;

}</source>

10 fd: 100

This program contains two functions: main() and f().

<source lang="cpp">#include <iostream> using namespace std;

void f(); // f"s protoype

int main() {

 cout << "In main()\n"; 

 f(); // call f() 

 cout << "Back in main()\n"; 

 return 0; 

}

// This if the function"s definition. void f() {

 cout << "Inside f()\n"; 

}</source>

In main()
Inside f()
Back in main()