Difference Between Local and Global Variables (With Table)

Since computers have become a huge aspect of our lives now and, as we all are aware of, have enslaved us, it never hurts to know a few of its details that generally help us on a day-to-day basis. To delve into a topic that is quite technical and deep, we should take a look at the concept of variables and the difference between its types- local and global.

Local vs Global Variables

The difference between Local and Global Variables is that though both are two types of variables, the former happens to be declared inside the function, whereas the latter is declared outside of it. Their lifetimes differ too. While the former’s life starts and ends with the function’s execution and termination, the latter is created even before the program’s execution is started. However, it ends with the termination of the program.

A local variable happens to be a kind of variable. It is declared inside the function, and its lifetime ranges from its execution to its termination. Its scope is also limited within the function in which it has been declared. If it is uninitialized, then it can store the “garbage value”.

On the other hand, a global variable is also a type of variable. It is characterized by being declared outside the function. It is created even before the program’s execution begins; however, it ends with the termination of the program. If it is uninitialized, then it stores zero as default.

Comparison Table Between Local and Global Variables

Parameters of ComparisonLocal VariablesGlobal Variables
Data sharingThis is not possible here as the data can only be accessed by one functionAs multiple functions can access it, this feature is possible
ParameterPassing of parameters to access value is of utmost necessityPassing of parameters is not of utmost necessity as the value can be accessed all through
ModificationsIf the value is modified in one of the functions, then such modifications do not reflect in the other functionsIf the value is modified in one of the functions, then such modifications reflect all through the program
AccessibilityThis can be accessed through the statements contained inside a functionThis can be accessed through any statement that is there in the program
StorageThis is stored in an unspecified location unless specifiedThis is stored in a specified location

What are Local Variables?

This is a kind of variable. Its features are that it is declared within or inside a certain function, and the value of it can only be accessed by such statement that has been incorporated in the function. Its shelf-life commences when the execution of the program begins and ends with the termination of it.

Another aspect is that its scope is also limited within the function in which it has been declared. If it is uninitialized, then it can store the “garbage value”. For this, data sharing isn’t possible, this is because the data can only be accessed by one function. Also, the passing of parameters to access value is of utmost necessity.

Another factor that is to be noted is that if the value is modified in one of the functions, then such modifications do not reflect in the other functions. This can be accessed through the statements contained inside a function.

There are a few advantages of it, such as it guarantees that the values will be intact even when the task is running. As each task creates its local variable, the results will still be predictable. They are deleted with the completion of any function, thereby releasing the previously occupied memory space.

What are Global Variables?

This, too, is a kind of variable. It is characterized by being declared outside the function. It is created even before the program’s execution begins; however, it ends with the termination of the program. If it is uninitialized, then it stores zero as default.

Data-sharing is possible here because multiple functions can access it. This feature is possible. The passing of parameters is not of utmost necessity as the value can be accessed all through by virtue of the variables being declared outside the functions. If the value is modified in one of the functions, then such modifications reflect all through the program. This can be accessed through any statement that is there in the program.

There are certain advantages to it, such as it can be accessed from all the functions of the program. It is pivotal in storing “constants” and aids in maintaining consistency. This is the most useful when multiple functions access the same data. Its downsides are that several variables remain in the memory until the execution of the program, which in turn can lead to the “Out of Memory” problem. Furthermore, sometimes the results can be unreliable and unpredictable as the data can be changed or altered by any function.

Main Differences Between Local and Global Variables

  1. While Local Variables have acquired their name based on how they perform, that is, they are inside functions, Global Variables, too, have acquired their name from the fact that they are outside functions.
  2. The life of the variable for Local Variables commences with the execution of the program and ends with the termination of it. In contrast, the life of the variable in Global Variable commences even before the execution of the program. However, it ends with its termination.
  3. Local variables have their storage in unspecified stacks if they aren’t specified. On the other hand, Global variables’ storage is at a fixed location.
  4. Where the results produced in Local Variables have no scope for alteration, the results can be unreliable and unpredictable as the data can be changed or altered by any function in the case of Global Variables.
  5. While data-sharing cannot be possible in the case of Local Variables, it is just the opposite in the case of Global Variables.

Conclusion

As the intricacies in the world of computer increases, the confusion that springs from that will continue surfacing. This is why we should familiarize ourselves with the concept of variables and their types. Though both are two types of variables, the former happens to be declared inside the function, whereas the latter is declared outside of it. Their lifetimes differ too. While the former’s life starts and ends with the function’s execution and termination, the latter is created even before the program’s execution is started. However, it ends with the termination of the program. They have their own sets of advantages and disadvantages.

A few advantages of the former are that it guarantees that the values will be intact even when the task is running, and as each task creates its local variable, the results will still be predictable. In addition, certain advantages of the latter are that it can be accessed from all the functions of the program.

References

  1. https://onlinelibrary.wiley.com/doi/full/10.1111/cogs.12831
  2. https://www.sciencedirect.com/science/article/pii/S1878029615001905
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