Question

Write a function declaration and a function definition for a function that takes one argument of type int and one argument of type double, and that returns a value of type double that is the average of the two arguments

Short answer

Question: Write a function in C++ that takes one integer argument and one double argument, and returns the average of the two arguments as a double. Explain the function declaration and definition. Answer: The following function declares and defines a function called `average` that takes an integer and a double as arguments and returns their average as a double. ```cpp // Function declaration double average(int a, double b); // Function definition double average(int a, double b) { double sum = a + b; double avg = sum / 2; return avg; } ``` The function declaration specifies the return type (double), the function name (average), and its arguments' types (int and double). The function definition calculates the average of the two arguments by first adding the integer and double, creating a double result. Then, it divides the sum by 2 and returns the calculated average value, which is a double.

Step-by-step solution

Declare the function

First, we need to declare our function. The declaration should include the return type (double), the function name, and the types of its arguments (int and double). We can call our function "average". ```cpp double average(int a, double b); ```

Define the function

Now that we have declared our function, we need to provide the definition for it. The definition should include the function name, the types of its arguments, and the calculation of the average of the two arguments. ```cpp double average(int a, double b) { double sum = a + b; double avg = sum / 2; return avg; } ```

Explanation of the function definition

In the function definition, we first calculate the sum of the integer and double arguments. Since one of the arguments is a double, the result will also be a double. Afterwards, we divide the sum by 2 to find the average. Finally, we return the calculated average, which is of type double. Here is the final code for the function declaration and definition: ```cpp // Function declaration double average(int a, double b); // Function definition double average(int a, double b) { double sum = a + b; double avg = sum / 2; return avg; } ``` Now you can call this function with an integer and a double argument, and it will return the average of the two as a double.

Key concepts

Function Declaration

A function declaration in C++ introduces a function's name and describes its return type and parameter types, but without the body of the function. The declaration statement tells the compiler about the function's existence, its return value type, and the data types of its parameters.
For example, the declaration for a function that takes an integer and a double and returns a double would look like this: ```cpp double average(int a, double b); ```

• Return Type: This specifies the data type of the value that the function will return. In our example, the function will return a double.
• Function Name: This is the identifier used to call the function. We've named it average here.
• Parameters: The list inside the parentheses shows the data types and names of the variables that the function expects. Our function expects an int and a double.

Function declarations are essential because they enable the compiler to make sure function calls use the correct parameter types and number of arguments.
Declaration usually appears at the top of your code or in a header file.

Function Definition

A function definition provides the actual implementation of a function. It consists of opening with the function's return type and name, followed by a body enclosed in braces that contains the statements to execute the task. The function definition includes all the necessary code to perform the described functionality.
Continuing with our example of the average function, here's what the full definition looks like: ```cpp double average(int a, double b) { double sum = a + b; double avg = sum / 2; return avg; } ```

• After the function signature, the sum variable is calculated by adding the two arguments, a and b. Since one of the arguments is a double, the arithmetic will also be performed as doubles.
• The `avg` is calculated by dividing the sum by 2, producing the average value of the two parameters.
• The function returns this result, fulfilling its contract to return a double.

Inside the braces, this is where the function's logic is implemented. The definition should appear in a source file (.cpp) where the functionality is needed.

Data Types in C++

Data types in C++ determine the size and type of data that can be stored in a variable. Understanding different data types is crucial for writing effective programs as it influences how data is handled in memory.
In C++, the two primary data types we encounter in the function example are the int and the double:

• int: This is typically used for integer values. It occupies 4 bytes of memory and can store whole numbers without decimal places.
• double: This data type is for floating-point numbers, allowing decimal places. It uses 8 bytes of memory, which means it allows for more substantial and more precise numerical operations compared to int.

Different data types have specific uses, which can affect performance and memory usage, so selecting the appropriate type for a variable is essential.
By mixing these types in a function, such as taking both an int and a double parameter as in our example, C++ will perform type promotion ensuring calculations are performed accurately and data type requirements are maintained.