C Programming - Basics

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C Programming - Basics

Introduction

C programming language is a foundational tool in computer science, combining simplicity with the ability to perform complex and hardware-level operations. Below is an outline of the key basics of C programming:

Structure of a C Program

Every C program follows a defined structure comprising the following components:

1. Preprocessor Directives:
   Instructions to the compiler, starting with # (e.g., #include <stdio.h>).
2. Main Function:
   The entry point of a C program, where execution begins.
3. Statements and Expressions:
   Instructions written to perform specific tasks.
4. Return Statement:
   Ends the main() function and returns control to the operating system.

Example:

#include <stdio.h>                   // Preprocessor directive 

int main() {

      printf("Hello, World! \n");    // Print statement
   
     return 0;                      // Exit the program

  } 

Basic Syntax

• Case Sensitivity:
  C is case-sensitive (main is different from Main).
• Semicolon:
  Each statement ends with a semicolon (;).
• Comments:
  Used for documentation.
• Single-line: // Comment here
• Multi-line: /* Comment here */
• Curly Braces {}:
  Denote the beginning and end of blocks, such as functions.

Data Types

C provides a variety of data types to define variables:

• Basic Data Types:
• int: Integer numbers (e.g., 10, -5).
• float: Floating-point numbers (e.g., 3.14).
• double: Double-precision floating-point numbers.
• char: Single character (e.g., 'A').
• Derived Data Types:
• Arrays, Pointers, Structures, Unions.
• Void: Represents no value (e.g., void function).

Variables and Constants

• Variables:
  Used to store data values.

int age = 25;  // Variable declaration and initialization

• Constants:
  Immutable values defined using const or #define.

const float PI = 3.14;
#define MAX 100

Input and Output

• Input: Use the scanf() function.

int num;
scanf("%d", &num);  // Reads an integer input

• Output: Use the printf() function.

printf("Number is: %d", num);  // Prints the variable's value

printf("Number is: %d", num);  // Prints the variable's value

Operators

C supports various operators:

• Arithmetic Operators: +, -, *, /, %.
• Relational Operators: ==, !=, <, >, <=, >=.
• Logical Operators: &&, ||, !.
• Assignment Operators: =, +=, -=, etc.
• Bitwise Operators: &, |, ^, ~, <<, >>.

Control Flow

C provides control structures for decision-making and looping:

• Conditional Statements:
• if, else if, else.
• switch-case.
• Loops:
• for: For fixed iteration.
• while: For condition-based iteration.
• do-while: Executes at least once before checking the condition.

Example:

int i;
for (i = 0; i < 5; i++) {
    printf("%d ", i);  // Outputs 0 1 2 3 4
}

Functions

Functions are used to encapsulate reusable code blocks.

• Syntax:

returnType functionName(parameters) {
    // Code
    return value;
}

• Example:

int add(int a, int b) {
    return a + b;
}

Arrays

Arrays store multiple values of the same type.

int numbers[5] = {1, 2, 3, 4, 5};
printf("%d", numbers[2]);  // Outputs 3

Pointers

Pointers store memory addresses of variables.

int x = 10;
int *p = &x;  // Pointer to x
printf("%d", *p);  // Dereferences p to output 10

Strings

Strings are arrays of characters terminated by a null character (\0).

char name[] = "John";
printf("Name: %s", name);  // Outputs "John"

Memory Management

C provides dynamic memory allocation functions:

• malloc(), calloc() for allocation.
• free() for deallocation.

File Handling

C allows reading and writing to files using file pointers.

• File operations: fopen(), fclose(), fprintf(), fscanf().

FILE *fptr;
fptr = fopen("example.txt", "w");
fprintf(fptr, "Hello, File!");
fclose(fptr);