COMPUTER PROGRAMMING (CT 101) – Chapter 6

6.1.1 One Dimensional Array

A one-dimensional array is a linear list of elements.

• Declaration: data_type array_name[size];
  Example: int scores[50]; declares an integer array that can hold 50 scores.
• Initialization: Values can be assigned at declaration.
  Example: int numbers[5] = {10, 20, 30, 40, 50};
• Accessing Elements: Elements are accessed using a zero-based index. For the numbers array above, numbers[0] is 10 and numbers[4] is 50.

6.1.2 & 6.1.3 Two-Dimensional & Multi-Dimensional Array

A two-dimensional (2D) array can be seen as a table or matrix with rows and columns. A multi-dimensional array is an array of arrays.

• Declaration: data_type array_name[rows][columns];
  Example: int matrix[3][4]; declares a 2D array with 3 rows and 4 columns.
• Initialization: Can be done linearly or by grouping rows.
  Example: int table[2][3] = {{1, 2, 3}, {4, 5, 6}};

6.1.4 String & String Handling Functions

In C, a string is a one-dimensional array of characters terminated by a null character '\0'.

• Initialization: char greeting[] = "Hello"; (The compiler automatically adds `\0`).
• String Handling Functions (from <string.h>):
  • strlen(str): Returns the length of the string.
  • strcpy(dest, src): Copies the source string to the destination.
  • strcat(dest, src): Appends the source string to the end of the destination.
  • strcmp(str1, str2): Compares two strings. Returns 0 if they are equal.

6.1.5 Array of Strings

An array of strings is typically implemented as a 2D character array or an array of character pointers.

Example (using pointers): char *names[] = {"Alice", "Bob", "Charlie"};

6.2.1 Definition, Declaration & Types

• Declaration: data_type *pointer_name;
  Example: int *ptr;
• Address-of Operator (&): Gets the memory address of a variable.
• Indirection/Dereference Operator (*): Accesses the value at the address stored in a pointer.

int var = 20;
int *ptr;      // Declare an integer pointer
ptr = &var;    // Store the address of var in ptr
printf("Value of var: %d\n", *ptr); // Access value via pointer

Pointer Types:

• Void Pointer: void * can point to any data type but must be cast before dereferencing.
• Null Pointer: A pointer that points to nothing, usually initialized with NULL.
• Bad Pointer: An uninitialized pointer that holds a garbage address. Dereferencing it leads to undefined behavior.
• Pointer to Pointer: A pointer that stores the address of another pointer (e.g., int **ptr;).

6.2.2 Pointer Arithmetic

You can perform a limited set of arithmetic operations on pointers.

• Valid: Incrementing (++), decrementing (--), adding an integer, subtracting an integer, and subtracting two pointers of the same type.
• Invalid: Addition of two pointers, multiplication, or division.

When an integer is added to a pointer, the pointer is incremented by integer * sizeof(data_type) bytes.

6.2.3 Relationship between Pointer and Array

In C, an array name acts as a constant pointer to its first element.

• array_name is equivalent to &array_name[0].
• array_name[i] is equivalent to *(array_name + i).

This relationship allows you to use pointer syntax to access and manipulate array elements, which can be more efficient.