Pointers in C++

ARRAYS 

An array is a collection of identical data objects which are stored in consecutive memory locations under common variable name. An array must be declared before it is used in C + + program. The general form for declaration of an one dimensional array is : 

Storage - class data - type array - name [expression];  

The storage class can be either external, static or automatic. The ‘data-type’ is data type of elements of array. The entire array can be passed onto a function in C ++.An array name can be used as an argument for the function declaration.  

For example : int sumarray (int a [ ] , int n) ;    

                       sum= sumarray (a, n);  

Multidimensional Arrays 

Multidimensional arrays are defined in same manner as one dimensional arrays, except that a separate pair of square brackets are required for each subscript. A two dimensional array will require two pairs of square brackets. The general form of multidimensional array is: 

Storage-class data-type array-name [exp 1] [exp 2) ...... [exp n]; 

Pointers & It’s Advantages 

A pointer is a variable which holds the memory address of another variable. Pointers offer several advantages: they allow passing variables, arrays, functions, strings, and structures as function arguments; enable returning structured variables from functions; support dynamic memory allocation and deallocation; facilitate variable swapping without moving them; and establish links between data elements or objects. 

Pointers and functions 

The use of pointers in a function definition may be classified into two groups: 

1.  call by value: When a function is called, control will be transferred to it and the value of actual arguments are copied to the function. Any change made done by the function to a variable will not reflect in the variable of main function  
2. call by reference: In call by reference, when a function is called by a program the address of the actual arguments are copied onto the formal arguments e. the formal and actual arguments are referencing to same memory location. Therefore change in value of formal argument affects the value of actual arguments. The call by reference is used when function produces more than one value and provides these values to the caller.

Reference Parameters 

Arguments can be passed to function either by call by value or call by reference. By default C++ uses call by value. There are two ways to achieve call by reference.  

1. Explicitly pass a pointer to the (Discussed in Pointers & Functions)
2.  Use reference parameter: To create a reference parameter, we need to add ‘&’ before parameter's name. For example, void minus (int & i); 

Here i is a reference parameter. Now i becomes another name for whatever argument minus() is called with. Any operations that are applied to i affect the calling argument. 

Returning & Independent Reference 

A function may return a reference. It allows the function to be used on the left side of an assignment statement. 

 We can create independent reference, that is reference variable. It must be initialized at the time of declaration. 

 For example :            float total = 100;  

                                  float &sum= total; 

Strings & It’s functions 

Strings are one dimensional arrays of type char. In C + +, a string is terminated by a null character or '\0'. String constants are written in double quotes. The C++ compiler offers useful string handling functions like: 

Strlen(): This function counts the number of characters in the string. While calculating length, the function does not count the last null character. 

Strcpy (): This function copies the contents of one string into another. The base addresses of the source and target strings should be supplied to this function. 

Strcat (): This function joints the source string at the end of the target string. 

Strcmp (): 'strcmp()' compares two strings character by character. If they are identical, it returns zero; otherwise, it returns the numeric difference between the ASCII values of the first characters that do not match. 

These functions are in'string.h' header file. To use these functions, include 'string.h' in your program. 

Pointer is simply the address of a memory location and provides an indirect way of accessing data in memory. A pointer variable is defined to 'point to' data of a specific type.  

Declaration of a Pointer 

The value of a pointer variable is the address to which it points.(i.e. address of the memory location where variable is stored). For ex: 

int variable1; 

ptr1 = &variable1; 

The & operator returns a variable's memory address. Assigning &variable1 to ptr1 gives ptr1 the address of variable1. The * operator dereferences ptr1, accessing the value at that address, that is variable1. 

Pointer Arithmetic 

In C++, you can add or subtract integers from pointers, a practice known as pointer arithmetic. The result depends on the size of the object being pointed to.   You can compare two pointers of compatible type for equality (or inequality) 

Arrays & Pointers 

Arrays and pointers are closely related in C++. The compiler interprets the array name as the address of its first element. A pointer initialized to this address can traverse the entire array, functioning like an index.