Pointer Initialization Syntax and Operations
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2’nd Stage
(2020-2021)
Assist. Lec. Liqaa S.M.
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Syntax
Example:
int * a;
// pointer to an integer
double *da; // pointer to a double
float *fa; // pointer to afloat
char
*ch;
// character pointer
Data Type * Pointer variable name
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Syntax
Example:
void * vp;
// pointer to a void
Void * Pointer –variable name
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A null pointer is a regular pointer of any pointer type which has a
special value that indicates that it is not pointing to any valid reference
or memory address. This value is the result of type-casting the integer
value zero to any pointer type.
int * p;
p = 0; // p has a null pointer value
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Syntax
Example:
andy = 25;
fred = andy;
ted = &andy;
& Pointer variable name
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Example:
beth = *ted;
beth = ted; // beth equal to ted ( 1776 )
beth = *ted; // beth equal to value pointed by ted ( 25 )
difference between the reference and
dereference operators
& is the reference operator and can be read as "address of“.
* is the dereference operator and can be read as "value pointed by“.
Example:
#include <iostream>
using namespace std;
int main () {int firstvalue = 5, secondvalue = 15;
int * p1, * p2;
p1 = &firstvalue; // p1 = address of first value
p2 = &secondvalue; // p2 = address of second value
*p1 = 10; // value pointed by p1 = 10
*p2 = *p1; // value pointed by p2 = value pointed by p1
p1 = p2; // p1 = p2 (value of pointer is copied)
*p1 = 20; // value pointed by p1 = 20
cout << "first value is = " << firstvalue << endl;
cout << "second value is =" << secondvalue << endl;
return 0;
}
Result
first value is = 10
second value is = 20
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char a; // a has type char
char * b; // b has type char *
char ** c; // C has type char **
a = 'z'; // a has type char and a value of 'z'
b = &a; //b has type char* and a value of 7230
c = &b; // c has type char** and a value of 8092
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#include <iostream>
using namespace std;
int main () {int numbers[5];
int * p;
p = numbers;
*p = 10;
p++;
*p = 20;
p = &numbers[2];
*p = 30;
p = numbers + 3;
*p = 40;
p = numbers;
*(p+4) = 50;
for (int n=0; n<5; n++)
cout << numbers[n] << ", ";
return 0;
}
Result = 10, 20, 30, 40, 50
Pointers Arithmetic Operations
1.
Increment (++)
2.
Decrement (–)
3.
Pointer addition
4.
Pointer subtraction
Increment (++)
char *mychar;
short *myshort;
long *mylong;
mychar++;
myshort++;
mylong++;
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Syntax
return_type *Pointer function_name ( parameter list ) {body of the function
}
#include <iostream>
using namespace std;
int addition (int a, int b){return (a+b); }
int subtraction (int a, int b){return (a-b); }
int operation (int x, int y, int (*functocall) (int,int)) {int g;
g = (*functocall)(x,y);
return (g);
}
int main () {int m,n;
int (*minus)(int,int) = subtraction;
m = operation (7, 5, addition);
n = operation (20, m, minus);
cout <<n;
return 0; }
Pointer initialization involves syntax such as data type, variable name, and examples. Explore the usage of null pointers, reference operators, and dereference operators in C++. Understand the difference between reference and dereference operations through practical examples to better comprehend how pointers work in programming.
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Presentation Transcript
Lecture of Pointer Lecture of Pointer 2 nd Stage (2020-2021) Assist. Lec. Liqaa S.M.
1. 1. Initialization of Initialization of pointers pointers Syntax Data Type * Pointer variable name Example: int * a; // pointer to an integer double *da; // pointer to a double float *fa; // pointer to afloat char *ch; // character pointer
2 . Pointer void 2 . Pointer void Syntax Void * Pointer variable name Example: void * vp; // pointer to a void
3. Null 3. Null pointer pointer A null pointer is a regular pointer of any pointer type which has a special value that indicates that it is not pointing to any valid reference or memory address. This value is the result of type-casting the integer value zero to any pointer type. int * p; p = 0; // p has a null pointer value
Reference operator (&) Reference operator (&) Syntax & Pointer variable name Example: andy = 25; fred = andy; ted = &andy;
Dereference operator (*) Dereference operator (*) Example: beth = *ted; beth = ted; beth = *ted; // beth equal to ted ( 1776 ) // beth equal to value pointed by ted ( 25 )
difference between the reference and dereference operators & is the reference operator and can be read as "address of . * is the dereference operator and can be read as "value pointed by .
Example: #include <iostream> using namespace std; int main () { int firstvalue = 5, secondvalue = 15; int * p1, * p2; p1 = &firstvalue; p2 = &secondvalue; // p2 = address of second value *p1 = 10; // value pointed by p1 = 10 *p2 = *p1; // value pointed by p2 = value pointed by p1 p1 = p2; // p1 = p2 (value of pointer is copied) *p1 = 20; // value pointed by p1 = 20 cout << "first value is = " << firstvalue << endl; cout << "second value is =" << secondvalue << endl; return 0; } second value is = 20 // p1 = address of first value Result first value is = 10
Pointers to pointers Pointers to pointers char a; // a has type char char * b; // b has type char * char ** c; // C has type char ** a = 'z'; // a has type char and a value of 'z' b = &a; //b has type char* and a value of 7230 c = &b; // c has type char** and a value of 8092
Pointers and Pointers and arrays arrays #include <iostream> using namespace std; int main () { int numbers[5]; int * p; p = numbers; *p = 10; p++; *p = 20; p = &numbers[2]; *p = 30;
p = numbers + 3; *p = 40; p = numbers; *(p+4) = 50; for (int n=0; n<5; n++) cout << numbers[n] << ", "; return 0; } Result = 10, 20, 30, 40, 50
Pointers Arithmetic Operations 1. Increment (++) 2. Decrement ( ) 3. Pointer addition 4. Pointer subtraction
Increment (++) char *mychar; short *myshort; long *mylong; mychar++; myshort++; mylong++;
Pointers to functions Pointers to functions Syntax return_type *Pointer function_name ( parameter list ) { body of the function }
#include <iostream> using namespace std; int addition (int a, int b){ return (a+b); } int subtraction (int a, int b){ return (a-b); } int operation (int x, int y, int (*functocall) (int,int)) { int g; g = (*functocall)(x,y); return (g); } int main () { int m,n; int (*minus)(int,int) = subtraction; m = operation (7, 5, addition); n = operation (20, m, minus); cout <<n; return 0; }
