C Variables

Used to store and manipulate data.
Each variable can be decalred with a data type that decribes the values it can hold.
Syntax - Declaring a variable
data_type variable_name;

1. data_type - Specifies the data types that a variable can hold a value i.e; int, float, char, etc...
2. variable_name - Declares the name of the variale

Syntax - Initializing a variable
data_type variable_name = value;
Here we declare a value in view of the data type.

#include <stdio.h>

int main() {
    int age;  // Declaration
    age = 25; // Initialization

    float height = 1.75; // Declaration and initialization

    char grade = 'A';    // Declaration and initialization
    
    age = 19; // Modifiying a variable

    return 0;
}

We can modifiy the variables after we declared or intialize the value for the varibale.
While modifying the type of the value should be same.

Rules for Declaring Variable Names

To declare a variable name correctely here are some rules

#include <stdio.h>

int main() {
    int age;  // Declaration
    // Valid variable names
    int age;
    float average_score;
    char _grade;
    double temperature2;
    int counter123;
 
    // Invalid variable names 
    int 2ndPlace;        // Starts with a digit 
    char student-age;    // Contains invalid character '-' 
    double average mark; // Contains space 
    float if;            // Reserved keyword

    return 0;
}

Using Operators

We can use operators while assigning a value for the variable.
We can use addition, subraction, multiplication and more.

#include <stdio.h>

int main() {
    double PI = 3.14159;
    int radius = 5;
    int result = PI*radius;
    
    printf("The value is: %f\n", result);

    return 0;
}

Using Constants

Declaring a variable const make the variable values cannot be modified.
Syntax
const data_type CONSTANT_NAME = value;

#include <stdio.h>

int main() {
    const double PI = 3.14159;

    printf("The value of PI is: %f\n", PI);

    return 0;
}

Local and Global Variables

We can access varibales in two ways

1. Local Variables - Variables accessed with in a function or block
2. Global Variables - Varable accessed outside any function throughout the program

#include <stdio.h>

int globalVar = 10; // Global variable

int main() {
    int localVar = 5; // Local variable

    printf("Global variable: %d\n", globalVar);
    printf("Local variable: %d\n", localVar);

    return 0;
}

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