What key difference exists between functions and procedures?

The key distinction between functions and procedures lies in their ability to return values. Functions are designed to perform computations or operations and then return a value as a result. This means that any time a function is called, it produces an output that can be utilized in further calculations or decisions within the program. This output can often be used directly in expressions or assigned to variables.

In contrast, procedures are generally defined to perform a set of operations but do not provide a return value. While procedures can manipulate data and accomplish various tasks, they are not meant to return data directly to the point where they were called. They can be used to execute code that has side effects (like modifying variables or outputting to a screen) but they do not yield a result that is captured.

The understanding of this difference is fundamental in programming as it influences how data flows through a program, and helps developers choose the appropriate structure based on the desired result—whether they need a computation to return a value or simply to execute a task without returning anything.