Difference between revisions of "C-and-C++/C2/Scope-Of-Variables/English"

What is the Scope of variables.

What is a Global variable.

What is a Local variable.

Few examples.

We will also see some common errors and their solutions.

Ubuntu Operating System version 11.04,

gcc and g++ Compiler version 4.6.1

It is the region of code within which the variable can be accessed.

Depending on its type and place of declaration it is divided into two catagories:

Global Variable. And Local Variable.

#include<stdio.h>

I have already typed the program on the editor,

Let me open it.

scope.c

Let me explain the code now.

#include <stdio.h>

int a=5;

int b=2;

And we have initialized them by assigning values as 5 and 2.

A global variable is available to all functions in your program.

These are declared outside any functions above main() funtion.

These have a Global scope.

void add()

int sum;

sum = a+b;

It is declared inside the function add.

A local variable is available only to the function inside which it is declared.

These variables are declared inside a block.

These have local scope.

The sum of a and b will be stored in the variable sum.

printf("Sum is %d\n",c);

int main()

add();

return 0;

Ctrl, Alt and T keys simultaneously

gcc scope.c -o sco

To execute

Type

./sco

gcc space scope.c space -o space sco

And press Enter

To execute

Type

./sco

press Enter

Output

Sum of a and b is 7

Come back to our program

Click on Save as option

Type

.cpp

Now Save the file with an extension. .cpp and click on SAVE

iostream.

using namespace std;

Click on Save.

So no need to change anything.

cout <<

%d\n

Now delete the comma.

<<

Again type two opening angle brackets and within the double quotes type backslash n.

Now click on Save.

Let us execute the program.

g++ scope.cpp -o sco1

g++ space scope.cpp space -o space sco1

Here we have sco1 because we don't want to overwrite the output parameter sco for the file scope.c

Now press Enter.

./sco1

Type,

./sco1

And press Enter.

output

Sum of a and b is 7.

We can see that it is similar to our C code.

Type

int a = 2;

Come back to our program.

Suppose here I will declare variable a again,

Type

int a and a (semicolon) ;

We have declared the variable a above the main function.

And after the add function.

Let us see what happens.

Come back to the terminal.

Error

We see errors

Redifinition of int a

int a previously defined here.

Come back to our program.

a is a global variable.

It has a global scope.

We cannot declare the variable twice as it is already declared globally

We can only declare variable a as a local variable.

int a = 2;

Come back to our terminal.

Execute as before.

This brings us to the end of this tutorial.

In this tutorial we learnt,

Scope of variables

Global variable

eg. int a = 5; And

Local variable

eg. int sum;

Write a program to print the difference of two numbers.

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