Question

Resolve a problem with a function. Consider the following interactive session: Why do we not get any output when calling \(f(5)\) and \(f(10) ?\) (Hint: Save the \(\mathrm{f}\) value in a variable \(\mathrm{r}\) and write print \(\mathrm{r}\).)

Short answer

No output is shown because the function's return value isn't printed or captured in a variable.

Step-by-step solution

Define the Function

Before calling the function \(f\), ensure that it has been defined somewhere in the code. Without a function definition, any call to \(f(x)\) will result in an error or no output at all.

Check Function Return

Examine the function \(f\) to see if it returns any value. If \(f\) is missing a return statement or yields no output, calling it will produce no output as there is nothing for the function to send back.

Store the Function Output

Assign the output of the function \(f\) to a variable \(r\) as instructed: \( r = f(5) \). This step captures the result from calling the function.

Print the Result

To see the output of the function, use a print statement: \( \text{print}(r) \). This will send the stored value in \(r\) to the console, letting users visually check results.

Key concepts

Defining Functions

In order to solve a problem using a function, we must first define what the function does. A function is like a mini-program within a bigger program. It needs a name, parameters (if any), and a body where we define what the function actually performs. For example:

• def f(x): - This line of code defines a function named f that takes one parameter x.
• return x * 2 - The body of the function that performs an action, like multiplying x by 2.

Defining a function is crucial because it allows us to reuse code and make our programs more organized and readable. Whenever we call the function with specific arguments, the function executes its block of code and can return a result.

Function Return Values

Once a function does its job, it might need to send something back to the rest of the program. This is what the return statement is for. When a function reaches a return statement, it completes its execution and sends the specified value back to the caller. Consider this example:

• The function f(x) returns x * 2.
• When you call f(5), the function returns 10.

If a function lacks a return statement, it will return None by default, which is why you might not see any result when the function is called.

Variable Assignment

Variables are like containers to store data. After calling a function, you might want to store its return value in a variable. This is particularly important when you want to use the result in subsequent parts of your program.

• Example: r = f(5) stores the result of f(5) into the variable r.
• This means that r now holds the value 10, assuming f(x) returns x * 2.

Assigning function results to variables is a way to preserve and manipulate output within our programs effectively.

Print Statements

To see the results of your computations on the screen, you use print statements. This statement takes one or more arguments and sends them to the standard output, like a console or terminal.

• For instance, print(r) will display the value stored in r.
• If you don't print the result, it will stay hidden, even if the computation succeeded.

Using print statements is essential during debugging, as it helps us check whether our variables hold the right values and if our functions are behaving as expected. Print statements are one of the simplest but most effective tools for identifying the flow of a program.