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

In C++, the function signature is crucial as it tells us how the function should be invoked and what data types are involved. A function signature consists of the function's return type, the function's name, and the parameter list enclosed in parentheses.
For the exercise at hand, we want to create a function that calculates the sum of all integers smaller than a given integer. This function takes one integer parameter and returns an integer. As such, the function signature would look like this:
```cpp
int sumSmallerThan(int n);
```
Here:

• Return type is `int`, indicating that the function will return an integer value.
• Function name is `sumSmallerThan`, describing what the function does.
• Parameter list has one integer, `int n`, representing the upper boundary for our sum computation.

This signature helps other programmers understand how to use this function without diving into the implementation details.

A loop is a fundamental concept in programming used to repeat a block of code multiple times. C++ provides several types of loops, but the most basic one is the `for` loop. In our exercise, we use a `for` loop to iterate through all integers smaller than `n`.
Here is the loop within our function:
```cpp
for(int i = 0; i < n; i++) {
sum += i;
}
```

• The loop starts with `int i = 0`, initializing the loop variable `i` to 0.
• The condition `i < n` ensures that the loop continues as long as `i` is less than `n`.
• The expression `i++` increments `i` by 1 in each iteration of the loop.

Inside the loop, the line `sum += i` adds the current value of `i` to the `sum` variable. This process repeats until `i` reaches `n`. Using this loop, we iteratively accumulate the sum of all integers less than `n`, achieving our goal efficiently.

Parameters are integral to functions as they allow the passage of data into functions. In C++, a parameter specified within the parentheses of a function signature allows functions to operate with different values each time they are called.
For our function `sumSmallerThan`, we take one integer parameter `n`. This parameter dictates the upper bound of the numbers to be summed. Here's the full function implementation:
```cpp
int sumSmallerThan(int n) {
int sum = 0;
for(int i = 0; i < n; i++) {
sum += i;
}
return sum;
}
```
In the highlighted code portion, `int n` is our function parameter. This parameter decides the limit up to which we sum the integers. By calling `sumSmallerThan` with different values of `n`, you can compute different sums efficiently without changing the function's logic.
Understanding how to use parameters is vital as it allows functions to be flexible and reusable in varied scenarios.