C Programming: Pointers and Arrays

Pointers

• A pointer is a variable that stores the memory address of another variable.
• Declared using an asterisk (*) before the pointer name.
• Example: int *p;
• The address of a variable can be obtained using the unary operator (&).
• The value stored at a memory address can be accessed using the dereference operator (*).
• Example: int x = 10; int *p = &x; printf("%d", *p); // prints 10

Arrays

• A collection of values of the same data type stored in contiguous memory locations.
• Declared using square brackets ([]) after the array name.
• Example: int arr[5];
• Array elements can be accessed using their index (starting from 0).
• Example: arr[0] = 10;
• The size of an array is fixed and cannot be changed after declaration.

Data Types

• Primitive Data Types:
  • Integers: int
  • Floating Point Numbers: float, double
  • Characters: char
  • Boolean: No built-in boolean type, but can be represented using int (0 for false, 1 for true)
• Derived Data Types:
  • Arrays
  • Pointers
  • Structures
  • Unions
• Qualifier:
  • const: specifies that the value cannot be changed
  • volatile: specifies that the value can be changed by external factors
  • static: specifies that the variable is allocated storage only once

Functions

• A block of code that can be called multiple times from different parts of a program.
• Declared using the function name, return type, and parameter list.
• Example: int add(int a, int b) { return a + b; }
• Functions can take arguments, which are passed by value (a copy of the original value).
• Functions can return a value, which can be used in the calling code.
• Function Types:
  • Library Functions: predefined functions provided by the C standard library (e.g., printf(), scanf())
  • User-Defined Functions: functions defined by the programmer

Pointers

• A pointer stores the memory address of another variable.
• Declared using an asterisk (*) before the pointer name.
• The address of a variable can be obtained using the unary operator (&).
• The value stored at a memory address can be accessed using the dereference operator (*).

Arrays

• A collection of values of the same data type stored in contiguous memory locations.
• Declared using square brackets ([]) after the array name.
• Array elements can be accessed using their index (starting from 0).
• The size of an array is fixed and cannot be changed after declaration.

Data Types

Primitive Data Types

• Integers are represented using the int data type.
• Floating Point Numbers are represented using the float and double data types.
• Characters are represented using the char data type.
• Boolean values can be represented using int (0 for false, 1 for true).

Derived Data Types

• Arrays are a type of derived data type.
• Pointers are a type of derived data type.
• Structures are a type of derived data type.
• Unions are a type of derived data type.

Qualifiers

• The const qualifier specifies that the value cannot be changed.
• The volatile qualifier specifies that the value can be changed by external factors.
• The static qualifier specifies that the variable is allocated storage only once.

Functions

• A function is a block of code that can be called multiple times from different parts of a program.
• Declared using the function name, return type, and parameter list.
• Functions can take arguments, which are passed by value (a copy of the original value).
• Functions can return a value, which can be used in the calling code.

Function Types

• Library Functions: predefined functions provided by the C standard library (e.g., printf(), scanf()).
• User-Defined Functions: functions defined by the programmer.

Pointers in C

What is a Pointer?

• A pointer stores the memory address of another variable.
• It is a reference to a location in memory.

Declaring a Pointer

• Declare a pointer using the asterisk symbol (*) before the pointer name.
• Example: int *p; declares a pointer p that points to an integer variable.

Pointer Operations

• Assignment: Assign the address of a variable to a pointer using the unary operator (&).
• Dereferencing: Access the value stored at the memory address held by a pointer using the unary operator (*).
• Example: p = &x; assigns the address of x to p, and *p = 10; assigns 10 to the variable pointed to by p.

Pointer Arithmetic

• Increment: Increment a pointer using the increment operator (++), making it point to the next memory location.
• Decrement: Decrement a pointer using the decrement operator (--), making it point to the previous memory location.
• Example: p++ increments the pointer p to point to the next memory location, and p-- decrements the pointer p to point to the previous memory location.

Common Pointer Operations

• Pointer Comparison: Compare two pointers using relational operators (==, !=, , etc.).
• Pointer Addition: Add an integer to a pointer to increment its value, making it point to a different memory location.
• Example: p = p + 5; increments the pointer p to point to the memory location 5 units ahead.

Null Pointers

• A null pointer is a pointer initialized to zero.
• Example: int *p = NULL; declares a null pointer p.

Dangling Pointers

• A dangling pointer points to a memory location that has been freed or deleted.
• Example: free(p); frees the memory location pointed to by p, making p a dangling pointer.

Wild Pointers

• A wild pointer is an uninitialized pointer that points to a random memory location.
• Example: int *p; declares a wild pointer p.

Common Pointer Errors

• Dangling Pointer Error: Accessing a memory location that has been freed or deleted.
• Wild Pointer Error: Accessing a memory location through an uninitialized pointer.
• Null Pointer Error: Accessing a memory location through a null pointer.