Friday, January 12, 2007

Parkinson's LawParkinson's Law

““Work expands so as to fill Work expands so as to fill the time available for its the time available for its

completion."completion."

int main() { int *i; int i_array[4]={55, 26, 17, 68}; i=i_array; cout << i << " " << i_array << “\n”; cout << i[0] << " " << i_array[0] << “\n”; cout << *(i+1) << " " << i_array[1] <<“\n”; return 0;} //Output?

Pointers and Arrays

Output is:

0012FF6C 0012FF6C55 5526 26

Pointers and Arrays

int i1[4]={55,26,17,68};int i2[4]={11, 2, 53, 14};i2=i1; //NOT ALLOWED

char str1[]=“i am a string”;char str2[]=“i am a string”;str1==str2; //WRONG

Pointers may be compared in C++ using relational operators like >, >=, <, <=, == etc, but they must have some relationship to be meaningful

Pointers and Arrays

int i1[4]={55,26,17,68};int i2[4]={11, 2, 53, 14};i2=i1; //NOT ALLOWEDWhy? /*name of array is a constant that points to beginning of array*/

char str1[]=“i am a string”;char str2[]=“i am a string”;str1==str2; //WRONG way of string comparison

Pointers may be compared in C++ using relational operators like >, >=, <, <=, == etc, but they must have some relationship to be meaningful

Pointers and Arrays

int i1[4]={55,26,17,68};int i2[4]={11,2,53,14};

int *p1;p1 = i1;int *p2;p2 = p1; //this is ok

Pointers and Arrays

int *y_ptr, y;

//y is of type int

// y_ptr is pointer to int

y=45;

y_ptr=&y;

int *y_ptr, *another_ptr, y=45;

y_ptr=&y;

another_ptr=&y; /*what is *another_ptr

what is *y_ptr*/

SELF TEST: Pointers

int b[] = {10, 20, 30, 40}; int *bPtr; bPtr = b; // set bPtr to point to array b cout << "Array b printed with:" << endl << "Array subscript notation" << endl;

for (int i = 0; i < 4; i++) cout <<b[i] << endl;

cout << "Pointer subscript notation" << endl;

for (i = 0; i < 4; i++) cout << bPtr[i] << endl; //Another way to do this?

Using subscripting and pointer notations with arrays

int offset; cout << "Pointer/offset notation where" << endl << "the pointer is the array name" << endl;

for(offset = 0; offset < 4; offset++) cout << *(b + offset) << endl;

cout <<"Pointer/offset notation" << endl;

for(offset = 0; offset < 4; offset++) cout << *(bPtr + offset) << endl;

Using subscripting and pointer notations with arrays

int *i; int int_array[4]={5,6,7,8}; i=int_array;

cout << i << " " << int_array<<endl;

cout << i[0] << " " << int_array[0]<< endl ; cout << &i[0] << " " << &int_array[0]<< endl;

Using subscripting and pointer notations with arrays

0x0012FEBC 0x0012FEBC5 50x0012FEBC 0x0012FEBC

Using subscripting and pointer notations with arrays

int a[5]={12, 3, 45, 5, 8};int *ptr;ptr=a;cout<<a[0]<<endl;cout<<ptr[0]<<endl;cout<<*(a+0)<<endl;cout<<*(ptr+0)<<endl;

cout<<a[1]<<endl;cout<<ptr[1]<<endl;cout<<*(a+1)<<endl;cout<<*(ptr+1)<<endl;

SELF TEST: Using subscripting and pointer notations with arrays

int a[5]={12, 3, 45, 5, 8};int *ptr;ptr=a;cout<<a[0]<<endl; //prints 12

cout<<ptr[0]<<endl; //prints 12

cout<<*(a+0)<<endl; //prints 12

cout<<*(ptr+0)<<endl; //prints 12

cout<<a[1]<<endl; //prints 3

cout<<ptr[1]<<endl; //prints 3

cout<<*(a+1)<<endl; //prints 3

cout<<*(ptr+1)<<endl; //prints 3

SELF TEST: Using subscripting and pointer notations with arrays

int i1[4]={55, 26, 17, 68};What is wrong with the following statement?i1++;

//The following is okint *i_ptr;i_ptr = i1;i_ptr++;cout<<*i_ptr;

//The following is ok *(i1+3) = 100; // This is OK because i1 has not changed

Pointers and Arrays

int b[] = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100}; int *bPtr; bPtr= b; // set bPtr to point to array b /* set b2Ptr to point to sixth element of array b */ int *b2ptr; b2ptr = b+5; //Remember pointer arithmetic? cout << "b[" << 5 << "] = " << b[5] << endl; cout << "*b2ptr= " << *b2ptr << endl; cout << "(b2ptr - bPtr) = " << (b2ptr - bPtr);

Pointers and Arrays

int b[] = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100}; int *bPtr; bPtr= b; // set bPtr to point to array b /* set b2Ptr to point to sixth element of array b */ int *b2ptr; b2ptr = b+5; //Remember pointer arithmetic? cout << "b[" << 5 << "] = " << b[5] << endl; cout << "*b2ptr= " << *b2ptr << endl; cout << "(b2ptr - bPtr) = " << (b2ptr - bPtr) << endl;

Output is:b[5] = 60*b2ptr= 60(b2ptr - bPtr) = 5

Pointers and Arrays

int main() { int a[3]={10, 20, 30}; double b[3]={10.5, 20.5, 30.5}; int *i; double *f; int x, size=3; i = a; f = b; for(x=0; x<size; x++) { cout << i+x << " " << f+x << '\n'; cout <<*( i+x) << " " <<*( f+x) << '\n'; cout << *i+x << " " << *f+x << '\n'; } return 0; } //pointer-add example

Pointer Arithmetic

Output:0x0012FF74 0x0012FF5C10 10.510 10.50x0012FF78 0x0012FF6420 20.511 11.50x0012FF7C 0x0012FF6C30 30.512 12.5

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a; what is the difference between *i++ and (*i)++ and *(i++)?

cout<<(*i)++; // display and then increment pointee

cout<<++(*i); // increment pointee and then display

cout<<*(i++); // display and then increment pointer

cout<<*(++i); // increment pointer and then display

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<(*i)++; // value is incremented

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<(*i)++; // value is incremented

//prints 1

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<++(*i); // value is incremented

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<++(*i); // value is incremented

//prints 2

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<*(i++); // value is incremented

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<*(i++); // value is incremented

//prints 1

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<*(++i); // value is incremented

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a;

cout<<*(++i); // value is incremented

//prints 5

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a; What is output if the statement are executed one after the other? cout<<(*i)++; cout<<++(*i); cout<<*(i++); cout<<*(++i);

Pointer Arithmetic

int a[3]={1, 5, 9};int *i; i = a; What is output if the statement are executed one after the other? cout<<(*i)++; // 1 cout<<++(*i); // 3 cout<<*(i++); // 3 cout<<*(++i); // 9

Pointer Arithmetic

What is wrong here?

int* my_Ptr;*my_Ptr=32;

Self Test

int num[10];

int *start, *end;

start = num;

end = &num[9];

while(start!=end) {

cout << "Enter a number: ";

cin >> *start;

start++; }

start = num; /* reset the starting pointer */

while(start!=end) {

cout << *start << ' ';

start++; }

Comparing Pointers

int x[ ] = {1, 3, 5, 7, 9, 11};*x = *(x + *x) + *x;cout<<*x;

Pointers

int x[ ] = {1, 3, 5, 7, 9, 11};*x = *(x + *x) + *x;cout<<*x; // prints 4

Pointers

int *intPtr; int i[10]={10,11,12,13,14,15,16,17,18,19}; char *charPtr; char c[]="We are testing char pointers"; intPtr = i; charPtr = c; cout << i <<" "<< c << endl; cout << intPtr << " " << charPtr << '\n'; cout << *intPtr <<" "<< i[0] << '\n'; cout << *charPtr <<" "<< c[0] << '\n';

char pointers

0x0012FF54 We are testing char pointers0x0012FF54 We are testing char pointers10 10W W

char pointers

char n[25] = "Pointers Are Funny!!";

char *name, *temp;

name = n; temp = name+2;

cout << n << endl;

cout << name << endl;

cout << *name << endl;

cout << *(temp) << endl;

cout << n[10] << endl;

cout << ++name << endl;

cout << ++(*n) << endl;

cout << *(temp) << endl;

cout << ++name << endl;

cout << *name << endl;

cout << n + 15 << endl;

cout << name + 15 << endl;

cout << ++name << endl;

cout << name[2] << endl;

Make a memory drawing!

Pointers Are Funny!!Pointers Are Funny!!Pirointers Are Funny!!Qiinters Are Funny!!inny!!y!!nters Are Funny!!e

char n[25] = "Pointers Are Funny!!";

char *name;

name = n;

cout << n << endl;

cout << name << endl;

cout << *name << endl;

cout << *(name+2) << endl;

cout << n[10] << endl;

cout << ++name << endl;

cout << ++(*n) << endl;

cout << *(n+2) << endl;

cout << ++name << endl;

cout << *name << endl;

cout << n + 15 << endl;

cout << name + 15 << endl;

cout << ++name << endl;

cout << name[2] << endl;

Make a memory drawing!

Self Test