C Programming Tutorial
C Program Tutorial
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- C - Discussion
- C - Useful Resources
- C - Quick Guide
- C - Input & Output
- C - Typedef
- C - Bit Fields
- C - Unions
- C - Structures
- C - Strings
- C - Pointers
- C - Arrays
- C - Scope Rules
- C - Functions
- C - Loops
- C - Decision Making
- C - Operators
- C - Storage Classes
- C - Constants
- C - Variables
- C - Data Types
- C - Basic Syntax
- C - Program Structure
- C - Environment Setup
- C - Overview
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C Program Tutorial
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C - Scope Rules
C - Scope Rules
A scope in any programming is a region of the program where a defined variable can have its existence and beyond that variable it cannot be accessed. There are three places where variables can be declared in C programming language −
Inside a function or a block which is called local variables.
Outside of all functions which is called global variables.
In the definition of function parameters which are called formal parameters.
Let us understand what are local and global variables, and formal parameters.
Local Variables
Variables that are declared inside a function or block are called local variables. They can be used only by statements that are inside that function or block of code. Local variables are not known to functions outside their own. The following example shows how local variables are used. Here all the variables a, b, and c are local to main() function.
#include <stdio.h>
int main () {
/* local variable declaration */
int a, b;
int c;
/* actual initiapzation */
a = 10;
b = 20;
c = a + b;
printf ("value of a = %d, b = %d and c = %d
", a, b, c);
return 0;
}
Global Variables
Global variables are defined outside a function, usually on top of the program. Global variables hold their values throughout the pfetime of your program and they can be accessed inside any of the functions defined for the program.
A global variable can be accessed by any function. That is, a global variable is available for use throughout your entire program after its declaration. The following program show how global variables are used in a program.
#include <stdio.h>
/* global variable declaration */
int g;
int main () {
/* local variable declaration */
int a, b;
/* actual initiapzation */
a = 10;
b = 20;
g = a + b;
printf ("value of a = %d, b = %d and g = %d
", a, b, g);
return 0;
}
A program can have same name for local and global variables but the value of local variable inside a function will take preference. Here is an example −
#include <stdio.h>
/* global variable declaration */
int g = 20;
int main () {
/* local variable declaration */
int g = 10;
printf ("value of g = %d
", g);
return 0;
}
When the above code is compiled and executed, it produces the following result −
value of g = 10
Formal Parameters
Formal parameters, are treated as local variables with-in a function and they take precedence over global variables. Following is an example −
#include <stdio.h>
/* global variable declaration */
int a = 20;
int main () {
/* local variable declaration in main function */
int a = 10;
int b = 20;
int c = 0;
printf ("value of a in main() = %d
", a);
c = sum( a, b);
printf ("value of c in main() = %d
", c);
return 0;
}
/* function to add two integers */
int sum(int a, int b) {
printf ("value of a in sum() = %d
", a);
printf ("value of b in sum() = %d
", b);
return a + b;
}
When the above code is compiled and executed, it produces the following result −
value of a in main() = 10 value of a in sum() = 10 value of b in sum() = 20 value of c in main() = 30
Initiapzing Local and Global Variables
When a local variable is defined, it is not initiapzed by the system, you must initiapze it yourself. Global variables are initiapzed automatically by the system when you define them as follows −
| Data Type | Initial Default Value |
|---|---|
| int | 0 |
| char | |
| float | 0 |
| double | 0 |
| pointer | NULL |
It is a good programming practice to initiapze variables properly, otherwise your program may produce unexpected results, because uninitiapzed variables will take some garbage value already available at their memory location.
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