2 BytesC++ course_2014_c9_ pointers and dynamic arrays

Kinan keshkeh
IT Engineering-Damascus University
3rd year
Summer course- 2014
2 bytes team

Pointers
•A pointer is the memory address of a variable.
•If a variable holds numbers of Bytes then its address in memory is the address of the first byte !
•Pointer variable declarations : SYNTAX Type_Name *Variable_Name1, *Variable_Name2,. . .; EXAMPLE: double *pointer1, *pointer2;

Pointers
•A pointer is the memory address of a variable.
•If a variable holds numbers of Bytes then its address in memory is the address of the first byte !
•Pointer variable declarations : SYNTAX Type_Name *Variable_Name1, *Variable_Name2,. . .; EXAMPLE: double *pointer1, *pointer2;
Asterisk sign

Pointers
•void manipulatePointer(int *p); //Accepted but not as nice. int* p1, *p2; //Accepted but dangerous.
•void manipulatePointer(int* p); int *p1, *p2;

Pointers
•int* findOtherPointer(int* p);
Pointers can be Returned type

Pointers
42
42
v1 = 0;
p1 = &v1;
*p1 = 42;
cout << v1 << endl;
cout << *p1 << endl;

Pointers
42 42
v1 = 0;
p1 = &v1;
*p1 = 42;
cout << v1 << endl;
cout << *p1 << endl;

Pointers
•See the difference

Pointers
•MyType *p; p = new MyType;
•MyType *mtPtr; mtPtr = new MyType(32.0, 17); // calls MyType(double, int);
constructor
•If the type is a class type :

Pointers
•MyType *p; p = new MyType;
•MyType *mtPtr; mtPtr = new MyType(32.0, 17); // calls MyType(double, int);
•If the type is a class type :
•int *n; n = new int(17); // initializes *n to 17
•nonclass types

Pointers
int *p; p = new int; if (p == NULL) { cout << "Error: Insufficient memory.n"; exit(1); } delete p; //If new succeeded, the program continues from here.

Pointers
int *p; p = new int; if (p == NULL) { cout << "Error: Insufficient memory.n"; exit(1); } delete p; //If new succeeded, the program continues from here.
Memory ensuring

Pointers
int *p;
p = new int;
if (p == NULL)
{
cout << "Error: Insufficient memory.n";
exit(1);
}
delete p;
//If new succeeded, the program continues from here.
Free the memory location

typedef
•You can use typedef to define an alias for any type name or definition.
typedef double Kilometers;
………………… Kilometers distance;
•You can define a pointer type name so that pointer variables can be declared like other variables without the need to place an asterisk in front of each pointer variable.
………………… IntPtr p1,p2,p3;
typedef int* IntPtr;

ARRAYS & POINTERS
•The Array name is a pointer to the first of array , so you can use a pointer instead of array name ( but in the opposite way can’t )

Dynamic array
•Determine memory places as we need !
•The User would put its dimension from runtime .
Type *p;
p=new Type[n];

Dynamic array
Type *p;
p=new Type[n];
Double , float , char …

Dynamic array
Type *p; p=new Type[n];
It could be by « User »

Dynamic array
Type *p; p=new Type[n];
It could be by « User »
So it’s Dynamic !!!

Dynamic array
delete a [] ; « Illegal »

POINTER ARITHMETIC
•*(p + i) == p[i] *(p++) == p[i++] *(++p ) == p[++i] and the same if “ - “
•subtract tow pointers(the same type ) returns the number of the same type elements !

POINTER ARITHMETIC
#include <iostream> using std::cout; using std::endl; int main( ) { int a[] = {1, 2, 3, 4, 5}; int* b; b = a; for (int i = 0; i < 5; i++) cout << *(b+i) << " "; return 0 ; } /* The above is equivalent to the following: for (int i = 0; i < arraySize; i++) cout << b[i] << " "; */

Multi dimensional dynamic array !

Multi dimensional dynamic array
•It’s an Array of Array !
•To make an Array n * m
•We make an (m) array of pointers from the type ( T ) by “new”
•then from each pointer we make an (n) array of type ( T ) by “new”

#include <iostream>
using std::cin;
using std::cout;
using std::endl;
typedef int* IntArrayPtr;
int main( )
{
int d1, d2;
cout << "Enter the row and column dimensions of the array:n";
cin >> d1 >> d2;
IntArrayPtr *m = new IntArrayPtr[d1];
int i, j;
for (i = 0; i < d1; i++)
m[i] = new int[d2];
//m is now a d1-by-d2 array.
cout << "Enter " << d1 << " rows of "
<< d2 << " integers each:n";
for (i = 0; i < d1; i++)
for (j = 0; j < d2; j++)
cin >> m[i][j];
cout << "Echoing the two-dimensional array:n";
for (i = 0; i < d1; i++)
{
for (j = 0; j < d2; j++)
cout << m[i][j] << " ";
cout << endl;
}
for (i = 0; i < d1; i++)
delete[] m[i];
delete[] m;
return 0;
}

#include <iostream> using std::cin; using std::cout; using std::endl; typedef int* IntArrayPtr; int main( ) { int d1, d2; cout << "Enter the row and column dimensions of the array:n"; cin >> d1 >> d2; IntArrayPtr *m = new IntArrayPtr[d1]; int i, j; for (i = 0; i < d1; i++) m[i] = new int[d2]; //m is now a d1-by-d2 array. cout << "Enter " << d1 << " rows of " << d2 << " integers each:n"; for (i = 0; i < d1; i++) for (j = 0; j < d2; j++) cin >> m[i][j]; cout << "Echoing the two-dimensional array:n"; for (i = 0; i < d1; i++) { for (j = 0; j < d2; j++) cout << m[i][j] << " "; cout << endl; } for (i = 0; i < d1; i++) delete[] m[i]; delete[] m; return 0; }

Enter the row and column dimensions of the array:
3 4
Enter 3 rows of 4 integers each:
1 2 3 4
5 6 7 8
9 0 1 2
Echoing the two-dimensional array:
1 2 3 4
5 6 7 8
9 0 1 2

ARRAYS & classes
struct Record
{
int number;
char grade;
};
Record *p;
p = new Record;
p->number = 2001;
p->grade = ’A’; // <===========> (*p).grade=‘A’
•The operator “ -> “ :

ARRAYS & classes
class Sample
{
public:
...
void showStuff( ) const;
...
private:
int stuff;
...
};
•THE this POINTER :

ARRAYS & classes
void Sample::showStuff( ) const { cout << stuff; } //Not good style, but this illustrates the this pointer void Sample::showStuff( ) { cout << this->stuff; }

ARRAYS & classes
It is useful when you have a collision with another variable at the same namespace !

ARRAYS & classes
#include <iostream>
#include <cstdlib>
using namespace std;
class DayOfYear{
public:
void input( );
void output( );
void set(int month, int day);
void set(int month);
int getMonthNumber( );
int getDay( );
private:
int month;
int day;
};
void DayOfYear::set(int month, int day)
{
if ((month >= 1) && (month <= 12))
this->month = month;
else{
cerr << "Illegal month value! Program aborted.n";
exit(1);
}
if ((day >= 1) && (day <= 31))
this->day = day;
else{
cout << "Illegal day value! Program aborted.n";
exit(1);
}
}

Code discussion
Output Example :

Homework
• سؤال عممي :
ي ا رد بناء سمسمة خطية لمسيا ا رت لشركة ما حيث لكل سيارة
)رقم السيارة – تاريخ التسجيل (
• المطموب:
1 - كتابة اج ا رئية Insert لبناء السمسة بحيث يضاف المعطى
حسب الرقم بالمكان الصحيح
2 - كتابة اج ا رئية Print لطباعة بيانات السمسمة
3 - كتابة تابع يقوم بالبحث عن عنصر حسب الرقم
4 -كتابة تابع يقوم بمقارنة تاريخين
5 - طباعة السيا ا رت المسجمة قبل تاريخ معين بالاستعانة بالتابع
السابق

That’s for today
That’s for today guys !!

That’s for today
Go and Play !
Bye Bye !

2 bytes team
Group : group link
Mobile phone- Kinan : 0994385748
Facebook account : kinan’s account
2 bytes team

2 BytesC++ course_2014_c9_ pointers and dynamic arrays

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2 BytesC++ course_2014_c9_ pointers and dynamic arrays