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A variable's scope refers to the portion of a program where the variable is accessible. It determines where the variable can be used, viewed, and modified within the program. There are two primary types of variable scope: global scope and local scope.

A variable with global scope is accessible throughout the entire program. These variables are usually declared outside functions or code blocks. When a variable is accessible from any part of the code, it is said to have global scope.

A variable with local scope is accessible only within a specific portion of the program where it is declared, such as within a function or a code block. Once the function or code block finishes executing, the variable is no longer accessible and can't be used or modified.

Let's look at an example that demonstrates the use of a global variable: ``` // Global variable declaration int global_variable = 10; void someFunction() { // Can access global_variable within the function cout << global_variable; } int main() { // Can access global_variable in the main function too cout << global_variable; someFunction(); } ``` In this example, the 'global_variable' is declared outside any function and is accessible within 'someFunction()' as well as in the 'main()' function, making it a global variable.

Now, let's look at an example that demonstrates the use of a local variable: ``` void localExample() { // Local variable declaration int local_variable = 5; // Can access local_variable within the function cout << local_variable; } int main() { localExample(); // Can NOT access local_variable here, it's not in the scope // cout << local_variable; // This line would result in an error } ``` In this example, the 'local_variable' is declared within the 'localExample()' function and is only accessible within that function. If we tried to access it within the 'main()' function, it would result in an error. By following these steps and understanding the differences between global and local scope, you can now better grasp the concept of variable scope in programming.