Question

Write a function declaration and a function definition for a function that takes three arguments, all of type \(i n t,\) and that returns the sum of its three arguments.

Short answer

Answer: To declare and define a function that takes three integers and returns their sum, follow these steps: 1. Declare the function using the return type 'int', a name such as 'sumOfThree', and three integer input arguments: ```cpp int sumOfThree(int a, int b, int c); ``` 2. Define the function by repeating the declaration and adding a pair of curly braces '{ }' with instructions for computing the sum and returning it inside: ```cpp int sumOfThree(int a, int b, int c) { int sum = a + b + c; return sum; } ``` The function 'sumOfThree' is now complete and can be called with three integer arguments to find their sum.

Step-by-step solution

Declare the function

To declare the function, first determine the function's return type, which should be an integer since we are returning the sum of three integers. Next, choose a name for the function, for example, 'sumOfThree'. Then, specify the input arguments, which are three integers. Put all this information together to get the function declaration: ```cpp int sumOfThree(int a, int b, int c); ```

Define the function

Now that the function is declared, we need to define it to implement the sum operation. To do this, re-write the function declaration, and then add a pair of curly braces `{}` right after it. Inside the curly braces, write the instructions to compute the sum of the three input integers and return it. ```cpp int sumOfThree(int a, int b, int c) { int sum = a + b + c; return sum; } ``` The function is now complete, and it will successfully compute the sum of any three input integers when called with appropriate arguments.

Key concepts

Function Declaration

In C++, a function declaration is the initial step in indicating that there is a function somewhere in the program which can be called upon. Declaring a function involves stating its name, its return type, and what kind of inputs, known as parameters, it will accept. In this case, a function called `sumOfThree` is declared to take three integer parameters.

• The function's return type is specified first, which is `int`. This tells the program to expect an integer as the outcome of the function.
• Then comes the function name, like `sumOfThree`, giving the function a clear identifier.
• Lastly, the parameters are listed inside parentheses, using their type followed by a variable name: `(int a, int b, int c)`.

A function declaration looks like: ```cpp int sumOfThree(int a, int b, int c); ``` This indicates to the compiler that somewhere in the code, there will be a function defined that matches this signature.

Function Definition

After declaring a function, the next important step is defining it. Function definition provides all the operational instructions, implementing the core logic of the function. It tells the function what to actually do when it's invoked in the program.

• Start with the exact same syntax as the declaration. It needs to match exactly so that the compiler knows these are two parts of the same function.
• Follow it directly with a pair of curly braces `{}`.
• Inside these braces, write the code that performs the function’s task.

For our `sumOfThree` function definition: ```cpp int sumOfThree(int a, int b, int c) { int sum = a + b + c; return sum; } ``` Within the curly braces, the sum of the three integers is calculated and then returned, providing the main body of the function.

Integer Arguments

Functions often rely on input data to carry out their tasks, and these inputs are known as arguments. In the context of C++ functions, when we mention integer arguments, we're specifying that the function will take input data in the form of integers, which are whole numbers.

• Integer arguments are defined in a function's declaration and definition. This ensures that only numbers of this type are passed when the function is called.
• In our function, three integer parameters named `a`, `b`, and `c` are used as arguments. These act as placeholders for the actual input when the function is executed.
• The declared types help C++ manage memory efficiently and ensure type safety by matching the data types of provided arguments with expected parameters.

When calling `sumOfThree`, you need to provide three integers, like so: `sumOfThree(5, 10, 15)`, which will return the result 30. This example shows how integer arguments are practical and essential for computation.