Keywords, variable and constant in C programming

Published on : 2nd Oct 2021
Keywords : Keywords are reserved word in programming. Every keyword has a special meaning. 
Example : int, float, auto, static, extern etc.
Variables : A variable is a container which stores value. Keyword cannot be used as variable name. A variable name can be started as underscore(_) or an alphabet and then a combination of letters, undersciore(_) and alphabets. C programming is case-sensitive. So, UP and up will be considered as different variable names. We should give a readable and logical variable name.
Example :
Varible declaration :  int a;
When we do not initialize a variable, the variable stores garbage value.
variable initialization: a = 10;
Variable declaration with initialization : int a = 10;
Constant : A constant is a value or a variable whose value cannot be changed. We use "const" keyword to declare a variable as constant.
Example : 10, 10.444, const int a = 10;
Source Code :
#include <stdio.h>

int main(int argc, char** argv)
{
	int a = 10; // variable
	const int UP = 0; // constant
	a = 11;
	UP = 1;
	return 0;
}
Compilation message :
In function 'main': 
[Error] assignment of read-only variable 'UP'