Give one good reason that you should not use global variables in a program.

Using global variables in a program can lead to unintended side effects, making the code harder to read, understand, and maintain. A global variable can be accessed and modified from any part of the program, which may result in unexpected behavior if different parts of the code modify the variable without a clear understanding of its current state. This can make it difficult to track down bugs and understand the flow of data throughout the program. Suppose a global variable is used to store a value that is critical for multiple functions. If one function accidentally modifies the global variable's value, all other functions that depend on that value would be affected as well, leading to unexpected results and potential bugs. Additionally, global variables can lead to naming conflicts if multiple developers are working on the same project, and they both create a global variable with the same name for different purposes. These conflicts can result in one developer's code unintentionally affecting the other's work. In conclusion, avoiding the use of global variables can prevent unintended side effects, improve code readability and maintainability, and reduce the likelihood of bugs. Instead, it's better to use local variables with proper function parameters and return values to manage data within a program.