Variables are named reminiscence locations used to keep records in a laptop program. They act as containers that preserve values that can be manipulated and referenced in the course of this system’s execution.
Contents
Rules for defining variables in C
1.Valid Characters: Variable names can include letters (each uppercase and lowercase), digits, and underscores. but, the primary individual of a variable name must be a letter or an underscore. Variable names can be local characters or @, $, *, etc. It cannot contain special characters such as .
2. Case sensitive: C is case sensitive; This means that both uppercase and lowercase letters are treated equally. For example, age, Age, and AGE are treated as separate names.
3. Reserved keywords: Variable names cannot be the same as C keywords or reserved keywords. These expressions have a special meaning in C and are specific to certain functions. Examples of elements include int, glide, char, if, while, etc. takes place.
4.Length Limit: at the same time as there is no specific restriction at the duration of variable names in C, most compilers impose a limit. generally, the restrict is 31 characters, but this could range depending on the compiler.
 5.Meaningful: Variable names must be significant and descriptive. They should replicate the motive or content of the facts they constitute. This complements code clarity and makes it less difficult for different programmers (or yourself) to apprehend the code later on.
6.No Spaces: Variable names can’t include areas. in case you need to symbolize a multi-word variable call, you can use underscores or capitalize the first letter of each word after the first (e.g., my_variable, student Age, total_Amount, etc.).
7.Start with a Letter or Underscore: Variable names have to start with a letter (uppercase or lowercase) or an underscore (_). while starting with an underscore is authorized, it’s common exercise to avoid it except you’re writing gadget-level code.
8.No Leading Digits: Variable names can not begin with a digit. they can incorporate digits, however not as the first individual. as an instance, age2 is a valid variable name, but 2age isn’t
Types of Variables in C
1.Local variables:
local variables are declared in a function or code block and can only be accessed from that function or code        block.
Syntax
data_type variable_name;
Example
#include <stdio.h>
void myFunction() {
int num = 10; // Local variable
printf(“Local variable: %d\n”, num);
}
int main() {
myFunction();
return 0;
}
2. Static variables:
static variables retain their value between calls and have a local
Syntex
static data_type variable_name;
Example
#include <stdio.h>
void myFunction() {
static int count = 0; // Static variable
count++;
printf(“Static variable: %d\n”, count);
}
int main() {
myFunction();
myFunction();
myFunction();
return 0;
}
3.Global variables:
global variables are declared outside each function and can be accessed throughout the
Syntax
data_type variable_name;
Example
#include <stdio.h>
int globalVar = 20; // Global variable
void myFunction() {
printf(“Global variable: %d\n”, globalVar);
}
int main() {
myFunction();
return 0;
}
4. Automatic variables (also called local variables):
Automatic variables are declared in a function or code block and are created when entered into the function or code  They have a local area.
Syntax
data_type variable_name;
5. External variables:
External variables are declared outside all functions and can be accessed via multiple
Syntax
extern data_type variable_name;