Question

Write a short C++ function that takes an integer \(n\) and returns the sum of all the integers smaller than \(n\).

Short answer

Define function `sumBelow`, use a loop to calculate sum, and return the result.

Step-by-step solution

- Define the function signature

Start by defining the function signature. The function should be named `sumBelow`, and it will return an integer. It takes an integer parameter `n`.

- Initialize a sum variable

Inside the function, declare an integer variable named `sum` to store the cumulative sum. Initialize it to 0.

- Loop through integers smaller than `n`

Use a `for` loop to iterate through all integers from 1 to `n-1`. In each iteration, add the loop variable to `sum`.

- Return the result

After the loop ends, return the value of `sum`.

- Complete function definition

Combine all the steps to form the complete function definition.

Key concepts

Function Definition

In C++ programming, a function is a block of code that performs a specific task. Defining a function involves specifying the name of the function, the return type, and the parameters it takes. For example, a function to sum integers smaller than a given number can be defined as:
int sumBelow(int n).
This specifies that the function is named `sumBelow` and it returns an integer value while taking a single integer parameter `n`.
Function definitions are fundamental in organizing code and making it reusable.

For Loop

A `for` loop in C++ is used to iterate a block of code a specified number of times. It consists of an initialization, a condition, and an increment/decrement operation. In the context of summing integers smaller than `n`, a `for` loop helps to iterate through each integer starting from 1 up to `n-1`:
for (int i = 1; i < n; i++) { sum += i; }.
Here, the loop starts with `i = 1` and continues until `i` is less than `n`, incrementing `i` by 1 in each iteration. Inside the loop, the current value of `i` is added to the sum. `For` loops are very effective for problems that require repetitive tasks.

Integer Variables

In C++, an integer variable is declared using the `int` keyword. These variables store whole numbers. For example, in the `sumBelow` function, we need an integer variable `sum` to store the cumulative result:
int sum = 0;.
This line declares an integer variable `sum` and initializes it to 0.
Integer variables play a crucial role in many calculations and are one of the most commonly used data types in programming. They are utilized wherever you need to work with numbers without any fractional part.

C++ Programming

C++ is a powerful programming language that supports various programming paradigms, including procedural, object-oriented, and more. It is widely used for its efficiency and capabilities, especially in systems programming, game development, and performance-critical applications.
One of the strengths of C++ is its control over system resources and performance. By understanding and using constructs like functions, loops, and variables, one can write efficient and effective code.
The `sumBelow` function example consolidates these fundamental concepts, demonstrating how C++ can be utilized to solve a simple problem by summing integers smaller than a given number.