C Programming Language

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1 Third Year Diploma Courses in Electronics, Electronics & telecommunications Engineering Branch. C Programming Language As per MSBTE I Scheme Syllabus CPR Topic 5 Pointers Total Marks- 10 Contents: 6.1. Concepts of pointers, declaring, initialization, accessing 6.2. Pointers arithmetic 6.3. Handling array using pointers 6.4. Handling functions using functions Prof. Gunwant V. Mankar B.E(IT), M.Tech(CSE), AMIE, MIAEng, MSCI HOD in CSE Dept. (Somayya Dip. In Engg, Chandrapur) - info@gunwantmankar.com Website:-

2 5.1. Understanding Pointers Pointers-Def (Meaning )[S-15,W-15,W-16] Pointers are variables used to store the memory addresses of the variables. Variables store the values and pointers stores their addresses at which these variables are located. The values stored in the pointers are integer values Pointer declaration & initialisation [S-15,W-16] Likewise other variables pointer also needs to be declared. In declaration statement of pointer name of pointer variable is preceded by * (indirection operator) operator. Syntax:- data_type * name_of_variable Initialization: Syntax: pointer_variable_name = &variable_name; Ex. int a; int *p; p=&a; Ex. int *ptr ; Here ptr variable of data type integer pointer is declared as name of variable ptr is preceded by * (indirection operator) means that variable ptr is a pointer variable. Data type of pointer variable should similar to data type of variable of which it is going to store address Pointers are initialized by address of another variable& for accessing address of a variable address of operator is used. this operator will fetch address of variable to which it prefix (precedes). Ptr=&name_of_variable; 5.2. Example of integer and character pointer: [W-15] Integer pointer : int *ptr; int a=5; ptr = &a; Character pointer : char *p; char ch='x'; p=&ch; 5.3. * Operator [W-16,S-15] It is used to declare a pointer variable. CPR Page 2

3 Indirection operator * is used in C language to get the value stored at the address pointed by any pointer variable. It can also be used in pointer declaration just to indicate the type of the variable is a pointer type. For example1 : 1) int a, *ptr; //here a is any integer variable and ptr is an integer pointer. 2) a=5; // a is assigned value 5. 3) ptr=&a; // address of a is stored in ptr 4) printf( %d %d, a, *ptr); // will print the output as 5 5 as *ptr uses indirection operator to get the value stored at address pointed by ptr. Example2: int *ptr; The above statement declares ptr as an integer pointer variable. It is also used as value at operator i.e. it reads the value from the address stored in pointer variable. Example3: printf( %d, *ptr); The above statement displays value present at the address stored in ptr variable 5.4. & Operator[W-16] It is used to retrieve address of a variable from memory. Example: int *ptr,a; ptr=&a; The above statement stores the address of variable a in the pointer variable ptr Features of Pointers [S-15] Pointers provide direct access to memory Pointers provide a way to return more than one value to the functions Pointers can be used to pass information back and forth between the calling function and called function. Pointers allow us to perform dynamic memory allocation and deal location. Pointers helps us to build complex data structures like linked list, stack, queues, trees, graphs etc Advantages of Pointers[S-15, S-16] Pointers are more efficient in handling arrays and data tables. They can be used to return multiple values from a function via function arguments. Pointers permit references to functions and thereby facilitating passing of functions as arguments to other functions. The use of pointer arrays to character strings results in saving of data storage space in memory. Pointers allow C to support dynamic memory management. Pointers reduce length and complexity of programs. CPR Page 3

4 They increase the execution speed and thus reduce the program execution time Disadvantages of Pointers[S-16] If it contains an incorrect value it can lead to a problem when used. When you use this incorrect pointer to read a memory location, you may be reading a incorrect garbage value then error may be occurred in the program. Pointers are slower than normal variables. If pointers are updated with incorrect values, it might lead to memory corruption Array of Pointers[W-16,W-15] A pointer is a variable that contains an address which is a location of another variable in memory. Syntax to create an array of pointers: data type * arr_name[size]; Example: int *x[2]; char *name[3]= Nashik, Mumbai, Pune ; Program: #include<stdio.h> #include<conio.h> void main( ) char *str[5]= keyboard, monitor, CPU, harddisk, SMPS ; int i =0; clrscr( ); for(i=0;i<=4;i++) printf( \n %d element = %s,i,str[i]); getch(); Output- 0 element= keyboard 1 element=monitor 2 element=cpu 3 element=harddisk 4 element= SMPS Q. A program to show use of array of pointers.[s-16] Note:- You can write above program or following program # include<stdio.h> void main ( ) CPR Page 4

5 int *a[4]; int i=31, j=5,k=19,l=71,m; arr[0]=&i; arr[1]=&j; arr[1]=&k; arr[1]=&l; for (m=0; i<=3; m++) printf("%d", *(arr[m]); 5.9. use of pointer in array.[s-16] We can declare a pointer of type int to point to the array arr. int *p; p = arr; or p = &arr[0]; //both the statements are equivalent. Now we can access every element of array arr using p++ to move from one element to another. We can use a pointer to point to an Array, and then we can use that pointer to access the array Example: # include<stdio.h> void main( ) int i; int a[5] = 1, 2, 3, 4, 5; int *p = a; // same as int*p = &a[0] for (i=0; i<5; i++) printf("%d", *p); p++; In the above program, the pointer *p will print all the values stored in the array one by one use of (- ) operator with pointers[s-16] To access members of structure with pointer variable, we use arrow - in between pointer variable and structure member. Syntax : ptr - member of structure Arithmetic operations perform on pointer with example[s-16] int * i; i++; CPR Page 5

6 In the above case, pointer will be of 2 bytes. And when we increment it, it will increment by 2 bytes because int is also of 2 bytes. float * i; i--; In this case, size of pointer is still 2 bytes. But now, when we decrement it, it will decrement by 4 bytes because float is of 4 bytes. int *a,*b,*c; *a=10; *b=20; *c=*a * *b; printf( %d, *c); Here, Normal multiplication operation is done on pointer variables. int *a,*b,*c; *a=10; *b=20; *c=*a + *b; printf( %d, *c); Here, Normal addition operation is performed on pointer variables Important Programs 1) Write a program using pointer to swap the value of two integer numbers.[w-15] OR Write a program to exchange values of two variables using pointer[s-15] #include<stdio.h> #include<conio.h> void main() int a,b,*p1,*p2,temp; clrscr(); printf("enter the value of a:"); scanf("%d",&a); printf("enter the value of b:"); scanf("%d",&b); printf("\nvalues before swapping are: a=%d b=%d",a,b); p1=&a; p2=&b; temp=*p1; *p1=*p2; CPR Page 6

7 *p2=temp; printf("\nvalues after swapping are: a=%d b=%d",a,b); getch(); 2) Write a program to find product of two numbers using pointer[s-15] #include<stdio.h> #include<conio.h> void main( ) int *p1,*p2,a,b,mul; clrscr( ); printf("enter first no."); scanf("%d",&a); printf("enter second no."); scanf("%d",&b); p1=&a; p2=&b; mul=(*p1)*(*p2); printf("\nmultiplication is %d",mul); getch(); 3) Give the meaning of :- int *ptr; int a; ptr = &a;[w-15] int *ptr; :- Declaration of pointer variable ptr of integer data type. int a; :- Declaration of integer variable a. ptr= &a; :-Address of variable a is assigned to a variable ptr. 4) Explain meaning of following statement with reference to pointers. int * a, b; b = 20; * a = b; a = &b; [W-16] 1) int *a, b; It is declaring a basic int type variable b and a is declared as pointer to integer. 2) b = 20; It is storing value 20 to int variable b. CPR Page 7

8 3) *a = b; It is storing value of b at address stored in pointer a. 4) a = &b; It is storing address of b into pointer variable a. 5) Explain meaning of following statement with reference to pointers : Int p, x ; x = 10; p = x; P = &x; [S-15] Int *p, x; X=10; *p=x; P=&x; Given statements pointer p is declared. Value 10 is assigned to variable x.then content of x are copied to address which is currently held in p (garbage address ).in last statement address of x is copied in pointer p CPR Page 8

F.Y. Diploma : Sem. II [CO/CD/CM/CW/IF] Programming in C

F.Y. Diploma : Sem. II [CO/CD/CM/CW/IF] Programming in C Time : 3 Hrs.] Prelim Question Paper Solution [Marks : 70 Q.1 Attempt any FIVE of the following : [10] Q.1 (a) List any four relational operators.