Programming Techniques DT143G: Functions Lecture 6

Lecture 6: Functions

• The lecture is about functions in programming language, specifically focusing on programmeringsteknik DT143G.
• Functions are used to reuse code, increase readability, and manage complex code in a modular manner.
• Functions are like "black-boxes," where you define the input and the function does the processing, returning the desired output.

Today's Contents

• Functions
• Parameters
• Arguments

Why Functions?

• Functions are used to reuse code for different parts of a program.
• They improve code readability.
• Functions make it easier to manage bigger pieces of code.

Functions Overview

• Functions are key features of programming languages (except very basic ones).
• They are similar to mathematical functions.
• The format starts with return_type func_name(parameter_list) followed by the function body enclosed in curly braces.

Input, Output & Side Effects

• Input: A function can have zero or more inputs (parameters) of various types.
• Output: A function can return a value which is often stored in a variable. Some languages don't allow returning multiple values in a straightforward manner.
• Side Effects: These are any changes a function makes to the program's environment, like printing to the screen (e.g., using printf), altering global variables, or modifying memory locations.

Example

• An example was provided of a function called power (likely a function calculating an integer exponent of another integer).

Scope of Variables

• Variables inside a function (local variables) are only accessible inside that function.
• Arguments passed to functions are treated as temporary variables; changes inside the function don't affect the original variables outside.
• Global variables can be accessed from within a function; but it's better to avoid them unless necessary for a specific case.
• Example code was shown to demonstrate function scope in a program.

About Functions

• Functions can have different types of parameters, and possibly no parameters.
• Functions can return void (meaning no explicit value returned). Functions don't need a return with an explicit keyword.
• Functions need to be defined before being used.
• Header files (such as stdio.h or math.h) are essential if you use pre-defined functions in a program.

Side Effects

• In an ideal case, a function is considered a black box; it accepts input and generates output without impacting other parts of the program.
• External actions, such as printing to the console or writing to a file, are side effects.
• Changes to global variables and modifications to memory are also side effects.

Program Design

• Functions are the building blocks of a program, and are used to solve different parts of a problem.
• Program solutions can be generated by designing and implementing functions in a recursive way, i.e based on the functions used in the solution.

Conclusion

• Functions are crucial for writing organized, reusable, and understandable code.
• Be mindful of side effects and variable scope.
• Functions are a modular programming tool.