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Calling Functions

Explore how to invoke functions in C++ by passing parameters and managing return values. Understand how control transfers between caller and called functions to write organized and effective code.

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Calling refers to how a function is used in a code, i.e., how a function is invoked. To call a function, you write its name followed by the comma-separated list of actual input values in parentheses.

Code example

Let’s see how the existing functions are called in the main function.

C++
#include <iostream>
using namespace std;
void voidFunction();    // Declaring a void function
int getSum(int, int);   // Declaring a function that takes two int arguments and returns their sum
int main()
{
    int sum;
    voidFunction();        // Calling the function with the void return type
    sum = getSum(2,3);    // Calling the function getSum and saving the value returned in variable 'sum'
    cout << "The value of sum is: " << sum << endl;
    return 0;
}
void voidFunction()      // Writing the function definition
{
    cout << "This is a void function!" << endl;  // Function only prints a string
}
int getSum(int num1, int num2)    // Writing the function definition 
{
    // The value 2 has been passed as num1
    // The value 3 has been passed as num2
    return num1 + num2;      // Returning the sum of num1 and num2
}

Explanation

  • First, note the use of the two declarations that precede the main function. They allow main to use voidFunction and getSum even though they aren’t defined ...