Pointer Operations: A variable in a program has two attributes, value of variable and location of variable in the computer memory. Pointers are variables with value as location of another variable. Declare a pointer variable first and is been pointed to somewhere, and then value that a pointer variable points to is been manipulated. A simple declaration of a pointer is shown below: int *p; The above declaration defines the variable “p” as of the type pointer-to-int. Pointers are generated with “address-of” operator “&”, which is “pointer-to” operator. First an integer variable “i” is declared and then “p” is set to point to it as follows: int i = 6; p = &i; Sample Program: /********************************************************** * This program demonstrates the pointer assignments * * defining an integer variable i with a value and take * * p and q as pointers to integers. * **********************************************************/ //Select header file #include <iostream> using namespace std; #define NULL 0 main() function code to demonstrate the pointer operations. // Main function int main() { // value of “i” is assigned as 5 int i = 5; // Here “p” denotes a pointer to an integer int* p = NULL; // Here “q” denotes a pointer to an integer int* q = NULL; // Part(a)- No error, “p” is assigned as address of “i” p = &i; /*Part(b)- Error, “p” is assigned with contents at address of “i”.*/ p = *&i; /*Part(c)- Error, “p” is been assigned with value’s address that is stored at “i”.*/ p = &*i; /*Part(d)- No error, “i” is assigned with contents of address containing contents of “p”.*/ i = *&*p; /*Part(e)- Error, “i” is assigned with contents at address of “p”*/ i = *&p; /*Part(f)-Error, “i” is assigned with address of contents stored at “p”.*/ i = &*p; /*Part(g)-No error, “p” is assigned with address of contents present at address of “i”.*/ p = &*&i; /*Part(h)-Error, “q” is assigned with contents at address holding contents of “p”.*/ q = *&*p; /*Part(i)-Error, “q” is assigned with contents holding contents at address of “p”.*/ q = **&p; /*Part(j)-No Error, “q” is assigned with contents at address of “p”.*/ q = *&p; //Part(k)- No error, “q” is assigned with address holding contents of “p”.*/ q = &*p; return 0; } Compilation Errors: 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(10): error C2440: '=' : cannot convert from 'int' to 'int *' 1> Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(11): error C2100: illegal indirection 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(13): error C2440: '=' : cannot convert from 'int *' to 'int' 1> There is no context in which this conversion is possible 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(14): error C2440: '=' : cannot convert from 'int *' to 'int' 1> There is no context in which this conversion is possible 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(16): error C2440: '=' : cannot convert from 'int' to 'int *' 1> Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast 1>c:\users\300722\documents\visual studio 2013\projects\project1\project1\source.cpp(17): error C2440: '=' : cannot convert from 'int' to 'int *' 1> Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast a) Pointer assignments, p = &i; Here, “p” is assigned as the address of “i”, and the assignment does not cause compilation error. Hence, the result is . b) p = *&i; Here, “p” is assigned with contents at address of “i”. Contents cannot be stored at “p”. Also, here conversion from type “int” to “int*” is performed which is invalid and hence it results in . c) p = &*i Here, “p” is assigned with the address of value at “i”. Here, “i” is a variable, “i” is not holding address of any variable, and hence “i” could not be used as a pointer. also argument type of unary “*” is invalid in this case and hence it results in . d) i = *&*p; Here, “i” is assigned with contents of address containing contents of “p” and it does not cause produce error while compilation. Hence, the result is . e) i = *&p; This assignment results in an error while compilation, as “i” is assigned with contents at address of “p”. It address of “i” and it cannot be stored into integer variable “i”. Also, conversion from “int” to “int*” is performed here, that is invalid. Hence, the result is . f) i = &*p; This assignment causes an error while compilation as “i” is assigned with address of contents at “p”. Address cannot be stored into an integer variable “i”. Also, a conversion is performed from “int*” to “int” that is invalid. Hence, the result is . g) p = &*&i; Here, “p” is assigned with address of contents held at address of “i”. It does not cause an error while compilation. Hence, the result is . h) q = *&*p; This assignment causes an error while compilation, as “q” is assigned with contents at address holding contents of “p”, “q” can hold only address of variables because “q” is a pointer. In addition, conversion is performed from “int*” to “int” that is invalid. Hence, the result is . i) q = **&p; This assignment causes an error while compilation, as “q” is assigned with contents holding contents at address of “p”. Since, “q” is a pointer, it can hold only address. Also, a conversion from “int*” to “int” is performed, that is invalid. Hence, the result is . j) q = *&p; Here, “q” is assigned with contents at address of “p”. It does not cause an error while compilation. Hence, the result is . k) q = &*p; Here, “q” is assigned with address holding contents of “p”. It does not cause any error while compilation. Hence, the result is .

EBK DATA STRUCTURES AND ALGORITHMS IN C

4th Edition

ISBN: 9781285415017

Author: DROZDEK

Publisher: YUZU

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Concept of Pointer Parameter

Pointers are the special variable that stores the variable address, instead of storing the variable value. Pointer is a powerful feature of a programming language. A pointer is mostly used to save memory space and improve execution time.

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