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

Scope of variable.

Global variable.

Local variable.

We will do this with the help of example.

We will also see some common errors and their solutions.

Ubuntu Operating System version 11.04,

gcc and g++ Compiler version 4.6.1 on Ubuntu

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.

Local Variable.

#include<stdio.h>

I have already typed the code 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 value 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 scope.c -o sco

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

<stdio.h>

Type

<iostream>

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++ scope.cpp -o sco1

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

press Enter.

./sco1

Type,

./sco1

press Enter.

output

Sum of a and b is 9.

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

Type

int a = 2;

Suppose here I will declare variable a again,

Type

int a = 2;

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 an 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;

Local variable

eg. int sum;

Write a program to print the difference of two numbers.

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