Welcome to CISC220H

• Data Structures in C++

• sakai.udel.edu

• Office Hours: Mon/Wed 3:30PM - 4:30PM

• http://www.udel.edu/CIS/220/jatlas/09FH/

• TA: Adnan Ozsoy– ozsoy at cis.udel.edu

Who am I?

Who are you?

What will we learn?

• Pointers• Lists• Analysis/

Big O notation• Stacks• Queues• Trees

• Sorting• Hashing• Heaps• Graphs• NP-completeness

How will we learn?

• Class exercises (5%)

• Homework problems/programming (5*5%)

• Three programming projects (30%)

• Three tests (two midterm * 10%, final 20%)

What is “Honors”

• Labs– Normal lab part is optional (but required

knowledge)

• Projects– Pick a “fun” area at the beginning

• Class– Required discussion and participation– Cover same topics but in more depth

What is a Data Structure?

Objectives for Today

• Manipulate pointers– read/write– create– dereference– assign value

• Call functions– by value, by reference

• Reading - K+W P.1-P.6

Review of pointers & memory

cf. K&W, Chapter P

A C++ Primer

section P.5

Smith Hall • Newark, DE 19716 • USA

• How could we move the Department of Computer and Information Sciences?

Memory Address vs. Value Stored• Consider memory to be a single huge array:

– Each cell of the array has an address associated with it.

– Each cell also stores some value.

• Don’t confuse the address referring to a memory location with the value stored in that location.

23 42 ... ...101 102 103 104 105 ...

Pointers

• An address refers to a particular memory location. In other words, it points to a memory location.

• Pointer: A variable that contains the address of a variable.

z23 42 ... ...

101 102 103 104 105 ...

x y

Location (address)

name

104

Pointers• How to initialize a pointer:

– can initialize to NULL (i.e. not currently pointing to anything)

– & operator: get address of a variable

int *x;

x ? y ?

int y = 3; x ? y 3

x = &y; x y 3

Pointers• How to get the value that is pointed to?

– * “dereference operator”: get value pointed to• * x returns 3

• How to change the variable pointed to?– Use dereference * operator to left of =

x y 5

*x = 5;

x y 3

Functions

fx f(x)

Call-by-value

int sum(int x, int y) {

return x + y;

}

int main(void) {

cout << sum(5,6) << endl;

}

Call-by-reference

int sum(const int& x, const int& y) {

return x + y;

}

int main(void) {

cout << sum(5,6) << endl;

}

Group Review

• Break into teams of 4-5 students

• One person write an official answer

• Swap answers with a neighboring group and keep scores!

Question 1

• What is output from the following code:

double x = 5.5;

double *px = &x;

cout << *px << ‘\n’;

*px = 10.0;

cout << x << ‘\n’;

Question 2

• What is output from the following code:

double x = 5.5;

double y = 10.0;

double* px, py;

px = &x;

py = &y;

cout << *px << ‘\n’ << *py << ‘\n’;

Question 3

• What is output from the following code:

double x = 5.5;

double *px = &x;

*px = 3.14;

double& r = *px;

r = 99.44;

cout << x << ‘\n’;

Question 4

• What is output from the following code:void swap(int x, int y) {

int temp = x;

x = y;

y = temp;

}

int main(void) {

int a = 0;

int b = 5;

swap(a,b);

cout << a << endl;

}

Question 5

• Change the code to work correctly using pointers:void swap(int x, int y) {

int temp = x;

x = y;

y = temp;

}

int main(void) {

int a = 0;

int b = 5;

swap(a,b);

cout << a << endl;

}

Question 6

• What is the value of temp after each assignment?char blocks[3] = {'A','B','C'};

char *ptr = &blocks[0];

char temp;

/*1*/ temp = blocks[0];

/*2*/ temp = *(blocks + 2);

/*3*/ temp = *(ptr + 1);

ptr = blocks + 1;

/*4*/ temp = *ptr;

/*5*/ temp = *(ptr + 1);

Question 7

• What is the value of temp after each assignment?char blocks[3] = {'A','B','C'};

char *ptr = blocks;

char temp;

/*1*/ temp = *++ptr;

/*2*/ temp = ++*ptr;

/*3*/ temp = *ptr++;

/*4*/ temp = *ptr;

Question 8• Write code to reverse a string using only pointer arithmetic

(no array accessors):int main(void) {

char s[10] = "abcde";

for (int i = 0; s[i] != NULL; i++) {

cout << s[i];

}

revtString(s);

for (int i = 0; s[i] != NULL; i++) {

cout << s[i];

}

cout << ‘\n’;

return 0;

}