This document discusses pointers in C programming. It defines pointers as variables that contain the memory addresses of other variables. Pointers allow functions to modify variables in the calling function and facilitate dynamic memory allocation. The key pointer operators are asterisk (*) for dereferencing and ampersand (&) for getting a variable's address. Examples demonstrate declaring and using pointers, passing pointers to functions, pointers to structures, and the NULL pointer value. Pointer syntax and dereferencing must match the variable type to avoid errors.
Pointers are among C’s most powerful, yet most difficult concepts to master. Some tasks like dynamic memory allocation done only by using pointers. So it is essential to learn pointers.
Pointers are a type of variable, just like int, double, etc., except instead of storing a value, they store a memory address of another variable.
Memory management is one of the most fundamental and important aspect for any computer programming language. In the dynamic memory allocation, the memory is allocated to a variable or program at the run time.
In computer science, a pointer is a programming language object, whose value refers to (or "points to") another value stored elsewhere in the computer memory using its memory address. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer.
A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before you can use it to store any variable address.
There are few important operations, which we will do with the help of pointers very frequently. (a) we define a pointer variable (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand.
This Presentation gives you all knowledge about #CPointers, #PointersInC.
The given slides are as follows:
1. Introduction of Pointers.
2. Systems to create a pointer in C.
3. Valid Pointer Examples in C.
4. Graphical representation of address assigning in c using pointer.
5. 1st Sample program of pointers in C.
6. Types of Pointers
7. NULL Pointer in C (Types of Pointer)
8. void Pointer in C (Types of Pointer)
9. Wild Pointer in C (Types of Pointer)
10. Changing value of variable using pointer
11. Update and Access value of variable using pointer in example.
12. Types of format specifies to print address in different format.
13. Advantages of Pointer in C.
14. Disadvantages of Pointer in C.
15. Pointers with Array using Programs. #pointerwitharray
16. Another Example of #pointerwitharray.
17. Relationship Between Arrays and Pointers.
18. Relationship Between Arrays and Pointers explanation with diagram.
19. Pointers and String. #PointersAndString
20. Function with Array Parameters using pointers.
21. Passing Pointers to Function or Pointer argument function. #PointerWithFunction
Pointers are among C’s most powerful, yet most difficult concepts to master. Some tasks like dynamic memory allocation done only by using pointers. So it is essential to learn pointers.
Pointers are a type of variable, just like int, double, etc., except instead of storing a value, they store a memory address of another variable.
Memory management is one of the most fundamental and important aspect for any computer programming language. In the dynamic memory allocation, the memory is allocated to a variable or program at the run time.
In computer science, a pointer is a programming language object, whose value refers to (or "points to") another value stored elsewhere in the computer memory using its memory address. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer.
A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before you can use it to store any variable address.
There are few important operations, which we will do with the help of pointers very frequently. (a) we define a pointer variable (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand.
This Presentation gives you all knowledge about #CPointers, #PointersInC.
The given slides are as follows:
1. Introduction of Pointers.
2. Systems to create a pointer in C.
3. Valid Pointer Examples in C.
4. Graphical representation of address assigning in c using pointer.
5. 1st Sample program of pointers in C.
6. Types of Pointers
7. NULL Pointer in C (Types of Pointer)
8. void Pointer in C (Types of Pointer)
9. Wild Pointer in C (Types of Pointer)
10. Changing value of variable using pointer
11. Update and Access value of variable using pointer in example.
12. Types of format specifies to print address in different format.
13. Advantages of Pointer in C.
14. Disadvantages of Pointer in C.
15. Pointers with Array using Programs. #pointerwitharray
16. Another Example of #pointerwitharray.
17. Relationship Between Arrays and Pointers.
18. Relationship Between Arrays and Pointers explanation with diagram.
19. Pointers and String. #PointersAndString
20. Function with Array Parameters using pointers.
21. Passing Pointers to Function or Pointer argument function. #PointerWithFunction
1. Introduction to Pointers:
- Pointers are variables that store memory addresses. They provide a way to directly manipulate memory, enabling efficient and flexible programming.
2. Pointer to Pointer:
- A pointer that holds the address of another pointer. Useful in scenarios where multiple levels of indirection are required.
3. Null Pointer, Generic Pointer, and Dangling Pointer:
- Discusses the concepts of null pointers (pointers with no valid address), generic pointers (void pointers), and dangling pointers (pointers pointing to released memory).
4. Passing an Array to a Function:
- Explains how to pass arrays to functions, emphasizing the use of pointers to efficiently work with arrays in functions.
5. Returning an Array from Function:
- Explores the technique of returning arrays from functions, often involving the use of pointers to manage memory.
6. Array of Pointers:
- Describes the concept of an array where each element is a pointer, enabling the creation of dynamic data structures.
7. Pointers and 1D Array:
- Examines the relationship between pointers and one-dimensional arrays, highlighting how pointers can be used for array manipulation.
8. Pointers and 2D Array:
- Discusses the use of pointers in managing two-dimensional arrays, which involves handling rows and columns efficiently.
9. Using Pointers for String Manipulation:
- Illustrates how pointers are employed for efficient manipulation of strings, emphasizing dynamic memory allocation for flexible string handling.
10. Two-dimensional Array of Strings:
- Explores the combination of pointers and arrays to handle two-dimensional arrays of strings.
11. Array of Pointers to String:
- Focuses on the concept of an array where each element is a pointer to a string, allowing for dynamic string management.
This presentation is a part of the COP2272C college level course taught at the Florida Polytechnic University located in Lakeland Florida. The purpose of this course is to introduce students to the C++ language and the fundamentals of object orientated programming..
The course is one semester in length and meets for 2 hours twice a week. The Instructor is Dr. Jim Anderson.
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Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
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2. What is a pointer
• In a generic sense, a “pointer” is anything that tells usIn a generic sense, a “pointer” is anything that tells us
where something can be found.where something can be found.
– Addresses in the phone book
– URLs for webpages
– Road signs
3. Java Reference
• In Java, the name of an object is a reference to that object.In Java, the name of an object is a reference to that object.
HereHere ford is a reference to a Truck object. It contains theis a reference to a Truck object. It contains the
memory address at which the Truck object is stored.memory address at which the Truck object is stored.
Truck ford = new Truck( );
• The syntax for using the reference is pretty simple. JustThe syntax for using the reference is pretty simple. Just
use the “dot” notation.use the “dot” notation.
ford.start( );
ford.drive( 23 );
ford.turn (LEFT);
4. What is a pointer ?
• In C, a pointer variable (or just “pointer”) is similar toIn C, a pointer variable (or just “pointer”) is similar to
a reference in Java except thata reference in Java except that
– A pointer can contain the memory address of any variable
type (Java references only refer to objects)
– A primitive (int, char, float)
– An array
– A struct or union
– Dynamically allocated memory
– Another pointer
– A function
– There’s a lot of syntax required to create and use pointers
5. Why Pointers?
• They allow you to refer to large data structures in a compactThey allow you to refer to large data structures in a compact
wayway
• They facilitate sharing between different parts of programsThey facilitate sharing between different parts of programs
• They make it possible to get new memory dynamically as yourThey make it possible to get new memory dynamically as your
program is runningprogram is running
• They make it easy to represent relationships among data items.They make it easy to represent relationships among data items.
6. Pointer Caution
• They are a powerful low-level device.They are a powerful low-level device.
• Undisciplined use can be confusing and thus theUndisciplined use can be confusing and thus the
source of subtle, hard-to-find bugs.source of subtle, hard-to-find bugs.
– Program crashes
– Memory leaks
– Unpredictable results
7. C Pointer Variables
To declare a pointer variable, we must do two thingsTo declare a pointer variable, we must do two things
– Use the “*” (star) character to indicate that the variable being
defined is a pointer type.
– Indicate the type of variable to which the pointer will point
(the pointee). This is necessary because C provides
operations on pointers (e.g., *, ++, etc) whose meaning
depends on the type of the pointee.
• General declaration of a pointerGeneral declaration of a pointer
type *nameOfPointer;
8. Pointer Declaration
The declarationThe declaration
int *intPtr;
defines the variabledefines the variable intPtr to be a pointer to a variable of typeto be a pointer to a variable of type
int.. intPtr will contain the memory address of somewill contain the memory address of some int
variable orvariable or int array. Read this declaration asarray. Read this declaration as
– “intPtr is a pointer to an int”, or equivalently
– “*intPtr is an int”
Caution -- Be careful when defining multiple variables on the sameCaution -- Be careful when defining multiple variables on the same
line. In this definitionline. In this definition
int *intPtr, intPtr2;
intPtr is a pointer to an int, but intPtr2 is not!
9. Pointer Operators
The two primary operators used with pointers areThe two primary operators used with pointers are
* (star) and(star) and && (ampersand)(ampersand)
– The * operator is used to define pointer variables and to
deference a pointer. “Dereferencing” a pointer means to use
the value of the pointee.
– The & operator gives the address of a variable.
Recall the use of & in scanf( )
10. Pointer Examples
int x = 1, y = 2, z[10];
int *ip; /* ip is a pointer to an int */
ip = &x; /* ip points to (contains the memory address of) x */
y = *ip; /* y is now 1, indirectly copied from x using ip */
*ip = 0; /* x is now 0 */
ip = &z[5]; /* ip now points to z[5] */
If ip points to x, then *ip can be used anywhere x can be used so in this
example *ip = *ip + 10; and x = x + 10; are equivalent
The * and & operators bind more tightly than arithmetic operators so
y = *ip + 1; takes the value of the variable to which ip points, adds 1
and assigns it to y
Similarly, the statements *ip += 1; and ++*ip; and (*ip)++; all increment
the variable to which ip points. (Note that the parenthesis are
necessary in the last statement; without them, the expression would
increment ip rather than what it points to since operators like * and
++ associate from right to left.)
11. Pointer and Variable types
• The type of a pointer and its pointee must matchThe type of a pointer and its pointee must match
int a = 42;
int *ip;
double d = 6.34;
double *dp;
ip = &a; /* ok -- types match */
dp = &d; /* ok */
ip = &d; /* compiler error -- type mismatch */
dp = &a; /* compiler error */
12. More Pointer Code
• Use ampersand (Use ampersand ( & ) to obtain the address of the pointee) to obtain the address of the pointee
• Use star (Use star ( * ) to get / change the value of the pointee) to get / change the value of the pointee
• UseUse %p to print the value of a pointer withto print the value of a pointer with printf( )
• What is the output from this code?What is the output from this code?
int a = 1, *ptr1;
/* show value and address of a
** and value of the pointer */
ptr1 = &a ;
printf("a = %d, &a = %p, ptr1 = %p, *ptr1 = %dn",
a, &a, ptr1, *ptr1) ;
/* change the value of a by dereferencing ptr1
** then print again */
*ptr1 = 35 ;
printf(“a = %d, &a = %p, ptr1 = %p, *ptr1 = %dn",
a, &a, ptr1, *ptr1) ;
13. NULL
• NULL is a special value which may be assigned to a pointerNULL is a special value which may be assigned to a pointer
• NULL indicates that this pointer does not point to any variableNULL indicates that this pointer does not point to any variable
(there is no pointee)(there is no pointee)
• Often used when pointers are declaredOften used when pointers are declared
int *pInt = NULL;
• Often used as the return type of functions that return a pointer toOften used as the return type of functions that return a pointer to
indicate function failureindicate function failure
int *myPtr;
myPtr = myFunction( );
if (myPtr == NULL){
/* something bad happened */
}
• Dereferencing a pointer whose value is NULL will result inDereferencing a pointer whose value is NULL will result in
program terminationprogram termination..
14. Pointers and Function Arguments
• Since C passes all primitive function arguments “by value” thereSince C passes all primitive function arguments “by value” there
is no direct way for a function to alter a variable in the callingis no direct way for a function to alter a variable in the calling
code.code.
• This version of theThis version of the swap function doesn’t work.function doesn’t work. WHY NOT?WHY NOT?
/* calling swap from somewhere in main() */
int x = 42, y = 17;
Swap( x, y );
/* wrong version of swap */
void Swap (int a, int b)
{
int temp;
temp = a;
a = b;
b = temp;
}
15. A better swap( )
• The desired effect can be obtained by passing pointers to theThe desired effect can be obtained by passing pointers to the
values to be exchanged.values to be exchanged.
• This is a very common use of pointers.This is a very common use of pointers.
/* calling swap from somewhere in main( ) */
int x = 42, y = 17;
Swap( &x, &y );
/* correct version of swap */
void Swap (int *px, int *py)
{
int temp;
temp = *px;
*px = *py;
*py = temp;
}
16. More Pointer Function
Parameters
• Passing the address of variable(s) to a function canPassing the address of variable(s) to a function can
be used to have a function “return” multiple values.be used to have a function “return” multiple values.
• The pointer arguments point to variables in the callingThe pointer arguments point to variables in the calling
code which are changed (“returned”) by the function.code which are changed (“returned”) by the function.
17. ConvertTime.c
void ConvertTime (int time, int *pHours, int *pMins)
{
*pHours = time / 60;
*pMins = time % 60;
}
int main( )
{
int time, hours, minutes;
printf("Enter a time duration in minutes: ");
scanf ("%d", &time);
ConvertTime (time, &hours, &minutes);
printf("HH:MM format: %d:%02dn", hours, minutes);
return 0;
}
18. An Exercise
• What is the output from this code?What is the output from this code?
void F (int a, int *b)
{
a = 7 ;
*b = a ;
b = &a ;
*b = 4 ;
printf("%d, %dn", a, *b) ;
}
int main()
{
int m = 3, n = 5;
F(m, &n) ;
printf("%d, %dn", m, n) ;
return 0;
}
4, 4
3, 7
19. Pointers to struct
/* define a struct for related student data */
typedef struct student {
char name[50];
char major [20];
double gpa;
} STUDENT;
STUDENT bob = {"Bob Smith", "Math", 3.77};
STUDENT sally = {"Sally", "CSEE", 4.0};
STUDENT *pStudent; /* pStudent is a "pointer to struct student" */
/* make pStudent point to bob */
pStudent = &bob;
/* use -> to access the members */
printf ("Bob's name: %sn", pStudent->name);
printf ("Bob's gpa : %fn", pStudent->gpa);
/* make pStudent point to sally */
pStudent = &sally;
printf ("Sally's name: %sn", pStudent->name);
printf ("Sally's gpa: %fn", pStudent->gpa);
Note too that the following are equivalent. Why??
pStudent->gpa and (*pStudent).gpa /* the parentheses are necessary */
20. Pointer to struct for functions
void PrintStudent(STUDENT *studentp)
{
printf(“Name : %sn”, studentp->name);
printf(“Major: %sn”, studentp->major);
printf(“GPA : %4.2f”, studentp->gpa);
}
Passing a pointer to a struct to a function is more
efficient than passing the struct itself. Why is this
true?