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# Pointers

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### Pointers

1. 1. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar Pointer in C++Pointer is a special variable, used to store the address of another variable of same data type. #include<iostream> #include<conio.h> a using namespace std; int main() 5 { int a; 10234 a=5; cout<<"n Value of a :"<<a; // 5 is the value stored at a cout<<"n Address of a :"<<&a; // 10234 is the address of variable a getch( ); return 0; }& :- is known as address operator* :- is known as value operator if it is operative on address, otherwise it behaves like a multiplication operatorArithmetic Operation on Pointer : Only allowed arithmetic operation is addition(+) and Subtraction(-) Program Output #include<iostream> #include<conio.h> using namespace std; int main() { int a; a=5; int *b; b=&a; cout<<"n Value of b :"<<b<<endl; b=b+1 ; // increase block size cout<<"n New value of b :"<<b<<endl; getch(); return 0; }Pointer of Pointer Program Output #include<iostream> #include<conio.h> using namespace std; int main() { int a; a=5; int *b; b=&a; int **c; c=&b; int ***d; d=&c; cout<<"n Address of ann"; cout<<"n Using &a :"<<&a; cout<<"n Using b :"<<b; cout<<"n Using *c :"<<*c; cout<<"n Using **d :"<<**d; cout<<"nnn Value of an"; cout<<"n Using a :"<<a; Page 1 of 11
2. 2. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar cout<<"n Using *(&a) :"<<*(&a); cout<<"n Using *b :"<<*b; cout<<"n Using **c :"<<**c; cout<<"n Using ***d :"<<***d; getch(); return 0; }Pointer as a function parameter Program Output // program to demonstrate call by pointer method #include<iostream> #include<conio.h> using namespace std; void change(int *a) // parameter as pointer { *a = *a+20; } int main() { int x=20; cout<<"n Value of x before function call:"<<x; change(&x); // passing parameter cout<<"n Value of x before function call:"<<x; getch(); return 0; }Pointer as a function Return type value Program Output #include<iostream> #include<conio.h> using namespace std; int* read(void) { int a; a=20; return(&a); } int main() { int *res; res = read(); // store retured address cout<<"n Value of a :"<<*res; cout<<"n Value of a :"<<*(read()); getch(); return 0; } Pointer and ArrayWhen an array is defined like int x[5]; // The memory block is as shown below X 100 102 104 106 108 The address of 0th index block is called BASE ADDRESS and it can be obtained by the followingmethods Page 2 of 11
3. 3. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar (a) x -> 100 (b) &x[0] ->100 (c) x+0 ->100 (d) 0+x ->100 (e) &0[x] ->100Processing array as a pointer without using any extra pointer variable Program Output // program to access array as a pointer #include<iostream> #include<iomanip> #include<conio.h> #include<math.h> using namespace std; int main() { int x[10],i; // input phase for(i=0;i<10;i++) { cout<<"Enter value :"; cin>>x[i]; } // output cout<<"n Output using as a pointer:n"; for(i=0;i<10;i++) cout<<setw(6)<<*(x+i); getch(); return 0; }Processing array as a pointer using extra pointer variable Program Output #include<iostream> #include<iomanip> #include<conio.h> #include<math.h> using namespace std; int main() { int x[10],i,*p; p= x; // assign base address to p // input phase for(i=0;i<10;i++) x[i]=rand(); // output for(i=0;i<10;i++) { cout<<setw(6)<<*p; p++; } getch(); return 0; } Page 3 of 11
4. 4. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander NagarAccessing pointer as an array Program Output #include<iostream> #include<iomanip> #include<conio.h> #include<math.h> using namespace std; void change(int *x) { int i; for(i=0;i<10;i++) x[i]=x[i]+20; } int main() { int x[10],i; // input phase for(i=0;i<10;i++) { cout<<"Enter value :"; cin>>x[i]; } // processing phase change(x); // output phase cout<<"n Modified List :"; for(i=0;i<10;i++) cout<<setw(6)<<x[i]; getch(); return 0; } Pointer & StringString : it is an array of character, which always terminates with NULL (‘0’). Char str[80]=”RAKESH”; // It’s allocation in stin is as follows 0 1 2 3 4 5 6 7 8 9 ……………………………………………………..79 R A K E S H 0101 102 103 104 105………………………………………………………………………… ………180 cout<<str; // Please note that only the base address of string has been given to cout // and cout is here print the whole string not the base address Result : RAKESHExample 2. char str[80]=”RAKESH”; cout<<*str; // now compiler try to print value stored at base address Result : ‘R’Example 3 char str[80]=”RAKESH”; cout<<*++str; // process nearest first Result : ‘A’ Page 4 of 11
5. 5. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander NagarExample 4 char str[80]=”RAKESH”; cout<<++*str; // process nearest first Result : ‘S’Example 5 char str[80]=”RAKESH”; cout<<++str; // print 101 address onward upto NULL Result : AKESH Pointers and Structure Assigning and Accesssing structure type Pointers #include<iostream> #include<conio.h> using namespace std; struct student { int roll; char name[30]; char address[60]; }; int main() { student s; student *s1; s1= &s; //input phase cout<<"n Enter roll no :"; cin>>s.roll; cout<<"n Enter name :"; cin>>s.name; cout<<"n Enter address :"; cin>>s.address; // output - using pointer variable cout<<"n Roll :"<<(*s1).roll; // s1->roll cout<<"n Nane :"<<(*s1).name; // s1->name; cout<<"n Address :"<<(*s1).address; // s1->address getch(); return 0; } Page 5 of 11
6. 6. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander NagarNew ( ) : This function is used to assign memory to a pointer variable from the available memory heap. The function is responsible to calculate no of bytes and types of data, required.Delete ( ) : This function is used to release assigned pointer memory to memory heap Accessing Pointer Variable using new( ) and delete ( ) function #include<iostream> #include<conio.h> using namespace std; struct student { int roll; char name[30]; char address[60]; }; int main() { student *s; s= new(student); //input phase cout<<"n Enter roll no :"; cin>>s->roll; cout<<"n Enter name :"; cin>>s->name; cout<<"n Enter address :"; cin>>s->address; // output - using pointer variable cout<<"n Roll :"<<s->roll; cout<<"n Name :"<<s->name; cout<<"n Address :"<<s->address; delete(s); getch(); return 0; }Self Referential Structure: A structure which can have a variable of it’s own type inside it’s declaration, then the structure is known as self referential structure.Example struct student { Int roll; ` student *s; }; Example of link list#include<iostream>#include<iomanip>#include<conio.h>using namespace std;struct node{ int info; node *ptr; };int main(){ node *x,*y,*temp ; x= NULL; int choice; do { system("cls"); cout<<"n 1. Add at beginning"; Page 6 of 11
7. 7. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar cout<<"n 2. Add at end"; cout<<"n 3. Delete from beginning"; cout<<"n 4. Display "; cout<<"n 5. Exit"; cout<<"nnn Enter your choice :"; cin>>choice; switch(choice) { case 1: if(x==NULL) { x = new(node); cout<<"n Enter value :"; cin>>x->info; x->ptr = NULL; } else { temp = new(node); cout<<"n Enter value :"; cin>>temp->info; temp->ptr = x; x = temp; } break; case 2: if(x==NULL) { x = new(node); cout<<"n Enter value :"; cin>>x->info; x->ptr = NULL; } else { y =x; while(y->ptr!=NULL) y = y->ptr; y->ptr = new(node); y = y->ptr; cout<<"n Enter value :"; cin>>y->info; y->ptr = NULL; } break; case 3: if(x==NULL) { cout<<"n Link List empty"; getch(); } else { temp =x; x = x->ptr; delete(temp); } break; case 4: if(x==NULL) cout<<"n Link list empty"; else { y = x; while(y!=NULL) { cout<<setw(6)<<y->info; y = y->ptr; Page 7 of 11
8. 8. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar } } getch(); break; case 5: break; default: cout<<"n Wrong Choice.... Try again"; getch(); } // end of switch statement }while(choice!=5);return 0;} LINK LIST EMPLEMENTED STACK#include<iostream>#include<iomanip>#include<conio.h>using namespace std;struct node{ int info; node *ptr; };class stack { node *x,*y,*temp; public: stack() // constructor to initialize variable { x= NULL; } void push(void); // function to add element void pop(void); // function to delete element void display(void); // function to display stack element };void stack::push(){ if(x==NULL) { x = new(node); cout<<"n Enter value :"; cin>>x->info; x->ptr = NULL; } else { temp = new(node); cout<<"n Enter value :"; cin>>temp->info; temp->ptr = x; x = temp; } return;}void stack::pop(void){ if(x==NULL) { cout<<"n Stack is empty"; getch(); } else Page 8 of 11
9. 9. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar { temp =x; x = x->ptr; delete(temp); } return; }void stack::display(){ if(x==NULL) cout<<"n Link list empty"; else { y = x; while(y!=NULL) { cout<<setw(6)<<y->info; y = y->ptr; } } return; }int main(){ stack S; int choice; do { system("cls"); cout<<"n S T A C K M E N U "; cout<<"n 1. Push"; cout<<"n 2. Pop"; cout<<"n 3. Display "; cout<<"n 4. Exit"; cout<<"nnn Enter your choice :"; cin>>choice; switch(choice) { case 1: S.push(); break; case 2: S.pop(); break; case 3: S.display(); getch(); break; case 4: break; default: cout<<"n Wrong Choice.... Try again"; getch(); } }while(choice!=4); return 0; } Link List Implemented queue#include<iostream>#include<iomanip>#include<conio.h>using namespace std;struct node{ Page 9 of 11
10. 10. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar int info; node *ptr; };class queue { node *x,*y,*temp; public: queue() // constructor to initliaze variable { x= NULL; } void add_element(void); // function to add element void delete_element(void); // function to delete element void display(void); // function to display stack element };void queue::add_element(){ if(x==NULL) { x = new(node); cout<<"n Enter value :"; cin>>x->info; x->ptr = NULL; } else { y = x; while(y->ptr!=NULL) y = y->ptr; y->ptr = new(node); y = y->ptr; cout<<"n Enter value :"; cin>>y->info; y->ptr = NULL; } return;}void queue::delete_element(void){ if(x==NULL) { cout<<"n queue is empty"; getch(); } else { temp =x; x = x->ptr; delete(temp); } return; }void queue::display(){ if(x==NULL) cout<<"n Queue is empty"; else { y = x; while(y!=NULL) { cout<<setw(6)<<y->info; y = y->ptr; Page 10 of 11
11. 11. Prepared By : Rakesh Kumar D.A.V.Centenary Public School Chander Nagar } } return; }int main(){ queue q; int choice; do { system("cls"); cout<<"n QUEUE M E N U "; cout<<"n 1. Add Element"; cout<<"n 2. Delete Element"; cout<<"n 3. Display "; cout<<"n 4. Exit"; cout<<"nnn Enter your choice :"; cin>>choice; switch(choice) { case 1: q.add_element(); break; case 2: q.delete_element(); break; case 3: q.display(); getch(); break; case 4: break; default: cout<<"n Wrong Choice.... Try again"; getch(); } }while(choice!=4); return 0; } Page 11 of 11