Flash cards
Review the key moves
What is the main idea behind C++ Variable Scope?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ myFunction() {Put the learning moves in the order that makes the concept easiest to apply.
Now that you understand how functions work, it is important to learn how variables act inside and outside of functions.
In C++, variables are only accessible inside the region they are created. This is called scope .
Local Scope
A variable created inside a function belongs to the local scope of that function, and can only be used inside that function:
Example
void myFunction() {
// Local variable that belongs to myFunction int x = 5; // Print the variable x cout << x;
}
int main() {
myFunction();
return 0;
}A local variable cannot be used outside the function it belongs to.
If you try to access it outside the function, an error occurs:
Example
void myFunction() {
// Local variable that belongs to myFunction int x = 5;
}
int main() {
myFunction();
// Print the variable x in the main function cout << x;
return 0;
}Global Scope
A variable created outside of a function, is called a global variable and belongs to the global scope .
Global variables are available from within any scope, global and local:
Example
// Global variable x int x = 5; void myFunction() { // We can use x here cout << x << "\n";
}
int main() {
myFunction();
// We can also use x here cout << x;
return 0;
}Naming Variables
If you operate with the same variable name inside and outside of a function, C++ will treat them as two separate variables; One available in the global scope (outside the function) and one available in the local scope (inside the function):
xHowever, you should avoid using the same variable name for both globally and locally variables as it can lead to errors and confusion.
In general, you should be careful with global variables, since they can be accessed and modified from any function:
xConclusion
To sum up, use local variables (with good variable names) as much as you can. This will make your code easier to maintain and better to understand. However, you may find global variables when working on existing C++ programs or while collaborating with others. Therefore, it is good to understand how the scope works and how to use it effectively to make sure your code is clear and functional.