Introduction to Arrays in C Programming

Fundamental Concepts

• Basic Data Types: int, float, char, double, etc.
• Variable Declaration: Example: int a = 5;
  • Variable a of type int is assigned a value of 5

Memory Representation of Variables

• Memory Layout: Memory can be visualized as a tape of bytes
  • Each byte = 8 bits
• Storing an int Variable: Typically takes 4 bytes
  • Example: int a = 5; takes 4 bytes in memory
  • Address allocation example: starting from 100 to 103

Binary Representation

• Integer to Binary: Decimal 5 in 32-bit binary is 000...0101
  • Stored across 4 bytes or 32 bits

Limitations of Single Variables

• Single Value Storage: A variable stores one value at a time
  • Example: int a = 5; updates to int a = 6; overwrites 5

Intro to Arrays

• Need for Arrays: Efficiently store multiple values
  • Example: Storing roll numbers of 60 students
  • Avoid multiple variable declarations

Array Declaration

• Syntax: datatype arrayName[size];
  • Example: int rollNumbers[60];
• Size Constraint: Size must be a constant
• Invalid Declarations: int a[]; or int a[n]; (without pre-defined constant n)

Types of Arrays

• 1D Arrays: Single row of elements
• 2D Arrays: Matrix-like structure
• Multi-dimensional Arrays: Generally not covered in this session

Array Initialization

• Compile-Time (Static): Specify values during declaration
  • Example: int a[5] = {6, 2, 4, 3, 0};
  • Stores values in continuous memory locations
  • Address: base address + index * data type size
• Run-Time (Dynamic): Specify values during program execution
  • Use loops and standard input functions like scanf

Array Memory Allocation

• Consecutive Memory Allocation: Memory allocated in continuous blocks
  • Example: int a[5]; allocates 20 bytes (5 elements * 4 bytes each)

Fixed Size Limitation

• Fixed Size: Size declared at compile time cannot be changed at run time
  • Example: int a[5]; cannot store 6 elements
• Dynamic Arrays: Concept to overcome fixed size (discussed later)

Accessing Array Elements

• Random Access: Efficiently access any element using index
  • Example: a[2] to access the third element
  • Formula: Base address + (index * data type size)
• Element Indexing: Typically starts at 0

Example Code for Run-Time Initialization

#include <stdio.h>

int main() {
    int a[5];
    printf("Enter the elements of the array:\n");
    for (int i = 0; i < 5; i++) {
        scanf("%d", &a[i]);
    }
    return 0;
}

Summary

• Arrays are fixed-size, sequenced collections of same data-type
• Methods to declare, initialize, and access arrays
• Fixed size is both a feature and a limitation
• Random access allows efficient retrieval of elements
• Detailed explanation of 1D arrays, brief mention of 2D and multi-dimensional arrays

Next Steps

• Detailed discussion on run-time initialization, traversal, and operations on 1D arrays
• Introduction to 2D arrays and their memory access patterns