C Programming Basics: Data Types, Variables, Operators & Input/Output

What is C Programming?

C is a procedural programming language used to write efficient programs. It was developed by Dennis Ritchie in 1972. C is the base for many modern languages like C++, Java, and Python.

Why Learn C?

• Used in system programming (OS, drivers, embedded systems).
• Teaches structured programming (clear logic, modular code).
• Fast execution and low-level memory access.

Basic Structure of a C Program

Every C program has two parts:

1. Preprocessor directives (start with #include).
2. Main function (main()), where execution begins.

#include <stdio.h>  // Preprocessor directive (includes standard I/O functions)
int main()         // Main function (execution starts here)
{
    printf("Hello, World!");  // Prints text
    return 0;  // Ends program successfully
}

How it works:

1. #include <stdio.h> → Includes library for input/output.
2. int main() → Entry point of the program.
3. printf() → Displays output on the screen.
4. return 0; → Indicates successful execution.

Data Types in C

Data types define what kind of data a variable can hold. C has basic and derived data types.

1. Basic Data Types

Example:

int age = 20;          // Integer
float temperature = 36.6;  // Floating-point
char grade = 'A';      // Character

Variables in C

A variable is a named storage location in memory that holds data.

Rules for Naming Variables:

1. Must start with a letter or underscore (_).
2. Can contain letters, digits, and underscores.
3. No spaces or special characters (except _).
4. Case-sensitive (age ≠ Age).

Example:

int student_age = 18;  // Valid
int 123age = 20;      // Invalid (starts with digit)
int my-age = 25;      // Invalid (hyphen)

Constants in C

Constants are fixed values that cannot be changed during program execution.

Types of Constants:

1. Literal Constants (direct values):

   int x = 100;  // Integer literal
   float pi = 3.14;  // Floating-point literal
   

2. Symbolic Constants (defined using #define):

   #define PI 3.14159  // PI is now a constant
   

Operators in C

Operators perform operations on variables and values.

1. Arithmetic Operators

Example:

int a = 10, b = 3;
int sum = a + b;      // 13
int diff = a - b;     // 7
int product = a * b;  // 30
int quotient = a / b; // 3 (integer division)
int remainder = a % b;// 1

Input and Output in C

1. printf() Function

Used to display output on the screen.

printf("Hello, %s! Your age is %d.", name, age);

• %s → String (text)
• %d → Integer
• %f → Float

Example:

#include <stdio.h>
int main()
{
    printf("Name: %s, Age: %d\n", "Rohan", 20);
    return 0;
}

Output:

Name: Rohan, Age: 20

2. scanf() Function

Used to take input from the user.

scanf("%d", &age);  // Takes integer input
scanf("%f", &salary); // Takes float input
scanf("%c", &grade); // Takes character input

Example:

#include <stdio.h>
int main()
{
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);  // Stores input in 'num'
    printf("You entered: %d", num);
    return 0;
}

Output:

Enter a number: 42
You entered: 42

Type Casting in C

Converts one data type to another.

double x = 5 / 2;  // x = 2.0 (integer division)
double y = (double)5 / 2;  // y = 2.5 (forced float division)

Solved Examples

Example 1: Basic Input/Output

#include <stdio.h>
int main()
{
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("Square of %d is %d", num, num * num);
    return 0;
}

Input:

Enter a number: 5

Output:

Square of 5 is 25

Example 2: Arithmetic Operations

#include <stdio.h>
int main()
{
    int a = 10, b = 3;
    printf("Sum: %d\n", a + b);
    printf("Difference: %d\n", a - b);
    printf("Product: %d\n", a * b);
    printf("Quotient: %d\n", a / b);
    printf("Remainder: %d\n", a % b);
    return 0;
}

Output:

Sum: 13
Difference: 7
Product: 30
Quotient: 3
Remainder: 1

NEB Board-Style Questions

Short Answer Questions

1. What is the difference between int and float in C?
2. Write a program to print your name and age using printf().
3. Explain the use of #include <stdio.h> in a C program.

Programming Questions

1. Write a C program to:
   • Take two numbers as input.
   • Calculate and print their sum, difference, product, and quotient.
2. Write a program to convert temperature from Celsius to Fahrenheit using the formula:

   F = (C × 9/5) + 32
   

True/False

1. scanf() is used for output in C. (False)
2. Variables must start with a digit. (False)
3. #define PI 3.14 is a symbolic constant. (True)

Exam Tip

1. Memorize basic data types (int, float, char, double) and their sizes.
2. Practice printf() and scanf() with different data types.
3. Understand operator precedence (e.g., * before +).
4. Always declare variables before use.
5. Use comments (//) to explain code in exams.
6. Check for common mistakes:
   • Forgetting & in scanf() (e.g., scanf("%d", num) → wrong; scanf("%d", &num) → correct).
   • Mixing = (assignment) with == (comparison).

flowchart TD
    A["Start"] --> B["Declare Variables"]
    B --> C["Take Input<br/>scanf()"]
    C --> D["Perform<br/>Calculations"]
    D --> E["Display Output<br/>printf()"]
    E --> F["End Program"]

A screenshot of a C program in a code editor (e.g., Code::Blocks or VS Code). (Image: Notepad++ Original: Don Ho Screenshot Photograph: User:WubTh, Public domain, via Wikimedia Commons)