C++ Function Examples

Real Life Example

To demonstrate a practical example of using functions, let’s create a program that converts a value from fahrenheit to celsius :

Example

// Function to convert Fahrenheit to Celsius
float toCelsius(float fahrenheit) {
  return (5.0 / 9.0) * (fahrenheit - 32.0);
}

int main() {
  // Set a fahrenheit value
  float f_value = 98.8;

  // Call the function with the fahrenheit value
  float result = toCelsius(f_value);

  // Print the fahrenheit value
  cout << "Fahrenheit: " << f_value << "\n";

  // Print the result
  cout << "Convert Fahrenheit to Celsius: " << result << "\n";

  return 0;
}

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C++ Pass Array to a Function

Pass Arrays as Function Parameters

You can also pass arrays to a function :

Example

void myFunction(int myNumbers[5]) {
  for (int i = 0; i < 5; i++) {
    cout << myNumbers[i] << "\n";
  }
}

int main() {
  int myNumbers[5] = {10, 20, 30, 40, 50};
  myFunction(myNumbers);
  return 0;
}

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C++ Functions – Pass By Reference

Pass By Reference

In the examples from the previous page, we used normal variables when we passed parameters to a function. You can also pass a reference to the function. This can be useful when you need to change the value of the arguments: Continue reading C++ Functions – Pass By Reference

C++ The Return Keyword

Return Values

The void keyword, used in the previous examples, indicates that the function should not return a value. If you want the function to return a value, you can use a data type (such as int, string, etc.) instead of void, and use the return keyword inside the function: Continue reading C++ The Return Keyword

C++ Multiple Parameters

Multiple Parameters

Inside the function, you can add as many parameters as you want:

Example

void myFunction(string fname, int age) {
  cout << fname << " Refsnes. " << age << " years old. \n";
}

int main() {
  myFunction("Liam", 3);
  myFunction("Jenny", 14);
  myFunction("Anja", 30);
  return 0;
}

// Liam Refsnes. 3 years old.
// Jenny Refsnes. 14 years old.
// Anja Refsnes. 30 years old.

Note that when you are working with multiple parameters, the function call must have the same number of arguments as there are parameters, and the arguments must be passed in the same order.

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C++ Default Parameters

Default Parameter Value

You can also use a default parameter value, by using the equals sign (=).

If we call the function without an argument, it uses the default value (“Norway”):

Example

void myFunction(string country = "Norway") {
  cout << country << "\n";
}

int main() {
  myFunction("Sweden");
  myFunction("India");
  myFunction();
  myFunction("USA");
  return 0;
}

// Sweden
// India
// Norway
// USA

A parameter with a default value, is often known as an “optional parameter“. From the example above, country is an optional parameter and "Norway" is the default value.

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C++ Function Parameters

Parameters and Arguments

Information can be passed to functions as a parameter. Parameters act as variables inside the function.

Parameters are specified after the function name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma: Continue reading C++ Function Parameters

C++ Functions

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

Functions are used to perform certain actions, and they are important for reusing code: Define the code once, and use it many times.

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C++ Dereference

Get Memory Address and Value

In the example from the previous page, we used the pointer variable to get the memory address of a variable (used together with the & reference operator). However, you can also use the pointer to get the value of the variable, by using the * operator (the dereference operator): Continue reading C++ Dereference