C Variables

C Variables: Storing Information

In C programming, a variable is a named storage location in the computer's memory used to hold data. Think of a variable as a container that holds a value, which can be changed (vary) during the execution of a program.

Before you can use a variable in C, you must declare it. Declaring a variable tells the compiler what type of data it will hold and what its name is.

1. Declaring Variables

To declare a variable, you must specify its data type followed by its name (identifier).

Syntax:

type variableName;

• type: Specifies the kind of data the variable will store (e.g., int for integers, float for floating-point numbers, char for characters).
• variableName: The unique name you give to the variable.

#include <stdio.h>

int main() {
  int age;        // Declares an integer variable named 'age'
  float salary;   // Declares a float variable named 'salary'
  char grade;     // Declares a character variable named 'grade'
  return 0;
}

2. Initializing Variables

You can assign a value to a variable at the time you declare it. This is called initialization.

Syntax:

type variableName = value;

#include <stdio.h>

int main() {
  int myNum = 15;            // Integer (whole number)
  float myFloatNum = 5.99;   // Floating point number
  char myLetter = 'D';       // Character
  // Printing variables
  printf("My number is %d\n", myNum);
  printf("My float is %f\n", myFloatNum);
  printf("My letter is %c\n", myLetter);
  return 0;
}

3. Naming Rules for Variables

When naming variables in C, you must follow these standard rules to ensure your code compiles:

1. Valid Characters: Names can contain letters (a-z, A-Z), digits (0-9), and underscores (_).
2. Starting Character: Names must begin with a letter or an underscore. They cannot start with a digit.
3. Case Sensitivity: Variable names are case-sensitive. myVar and myvar are considered two entirely different variables.
4. No Whitespace: Names cannot contain spaces or special characters like !, #, %, etc.
5. Keywords: You cannot use C reserved keywords (like int, return, if, while) as variable names.

Good Naming Conventions

While x and y are valid variable names, it's a professional practice to use descriptive names that indicate the variable's purpose.

• Good: studentAge, totalScore, isGameOver
• Bad: a, b1, tmp_val_2