Introduction to C++

Introduction to C++

Computer Science I

Q: What is C++ C++ is a compiled, object-oriented

language It is the “successor” to C, a procedural

language (the “++” is called the successor operator in C+

+)

C was derived from a language called B which was in turn derived from BCPL

C was developed in the 1970’s by Dennis Ritchie of AT&T Bell Labs

C++ was developed in the early 1980’s by Bjarne Stroustrup of AT&T Bell Labs.

Most of C is a subset of C++

People & ProgramsUser: an individual who runs, or

executes, a programProgrammer: an individual who

creates, or writes, a program

C++ Program

Consists of…Declarations

Define the use of various identifiers, thus creating the elements used by the program (computer)

StatementsOr executable statements,

representing actions the computer will take on the user’s behalf

Identifiers Names for various entities used in a

program; used for... Variables: values that can change

frequently Constants: values that never changes Functions: programming units that

represents complex operations Parameters: values that change

infrequently

Simple C++ Program#include <iostream.h>

int main()

{

// Declarations

// Statements

return 0;

}

Compiler directive: Tells the compiler what to do before compiling

This one includes source code from another file


int main()

{

// Declarations

// Statements

return 0;

}

Main function


int main()

{

// Declarations

// Statements

return 0;

}

Header for main function

States… data type

for the return value

identifier for function

list of arguments between parenthesis(none for this function)


int main()

{

// Declarations

// Statements

return 0;

}

Braces enclose the body of the function

They represent the start and end of the function


int main()

{

// Declarations

// Statements

return 0;

}

Declarations and statements

Main body of function (or main part)

“//” represents the start of a comment


int main()

{

// Declarations

// Statements

return 0;

}

Return statement

specifies the value the function returns

All (almost) declarations and statements end with a semi-colon “;”


int main()

{

// Declarations

// Statements

return 0;

}

This program doesn’t do anything!

Sample C++ Program#include <iostream.h>

void main()

{

int number;

cout << “Enter a number” << endl;

cin >> number;

cout << “You entered: “ << number << endl;

}

Variable declaration

The identifier number is declared as being of data type int, or integer


void main()

{

int number;


cin >> number;


}

coutthe output statement for C++

Note the direction of “<<“

endl represents an end-of-line


void main()

{

int number;


cin >> number;


}

cinthe input statement for C++

Note the direction of “>>”


void main()

{

int number;


cin >> number;


}

Did you copy this down?

You had better, since this will be the first program you’ll try!


void main()

{

int number;


cin >> number;


}

That means right now!

AssignmentAssignment is an operation that

assigns the value of an expression to a variable

Ex.Total = 2 + 3 + 5

First, the expresssion “2 + 3 + 5” is evaluated

Then, this value is assigned to the variable “Total”

Assignment When a variable is declared, space is

allocated in the computer’s memory for the variable

Each data type requires a different number of bytes in memory for storing a variable

int - 2float - 4double - 8char, bool - 1

AssignmentWhen a variable

is assigned a value, the value is placed into the variable’s memory location

10

Total

Total = 2 + 3 + 5;

Arithmetic OperationsAddition: 2 + 3Subtraction: 5 - 2Multiplication: 10 * 4Division: 12 / 3

Order of OperationsArithmetic expressions are

evaluated according to the following order of operations

At each level, operations are evaluated left to right

(1) Parenthesis, Functions(2) Multiplication, Division(3) Addition, Subtraction

ParenthesisParenthesis are used to alter the

order with which operations are evaluated

Ex.4 + 5 * 2 equals 14(4 + 5) * 2 equals 18

Here we go! Problem: To determine the average of

three numbers Task: Request, from the user, three

numbers, compute the average and the three numbers, and print out the original values and the computed average

Do it! You have 20 minutes!

FunctionsComputer Science I

Q: What is a function?A programming unitSimilar to mathematical functionsExample:

f(x) = x2 + 5x + 7For x = 2, f(2) = (2)2 =5(2) + 7 = 21

Q: What is a function? It has...

... arguments ... a name

(identifier) ... a value it

returns ... a bodyint foo(int x)

{int result;result = x*x + 5*x + 7;return result;}

Procedural AbstractionThink “Black Box” !When using a function, you only

need to be concerned with what it does, not how it does it

When writing a function, you need to be concerned with the how

Example: Cube it!int cubeIt(int x){

int result;result = x*x*x;return result;

}

int cubeIt(int x){

int result;result = x;result = x*result;result = x*result;return result;

}

PseudocodeLooks like a programming

languageHas all the structure of a

programming languageHas a verrrrrry loose syntax

PseudocodeExample:

function foo (x)result x2 + 5x + 7return result

That’s it!Sloppy, ain’t it?

Decision StatementsComputer Science I

Q: What is a decision?Something that represents a

branching point in a solutionOutcomes are often dependent on

initial conditions

Decisions in ProgramsWithout decision statements (or

other dynamic control structures), programs are static

Static programs do exactly the same things each time they are executed

Dynamic programs do not

Boolean AlgebraBased on values that are either

True or FalseTrue and False values are often

represented by 1’s and 0’s, respectively

Logical Operations: AndA BExpression is

True iff A and B are both true

T FT T FF F F

Logical Operations: OrA BExpression is

True if either A or B are True

Note: Also True when A and B are both True

T FT T TF T F

Logical Operations: Exercises

A = True, B = True, C = False1. A B2. A C3. A B C4. (A B) (A C)

Relational Operations A < B “A less than B” A > B “A greater than B” A = B “A equal to B” A B “A less than or equal to B”

“A not greater than B” A B “A greater than or equal to

B”“A not less than B”

A B “A not equal to B”“A less than or greater than

B”

Relational Operations: Exercises

A = 5, B = 3, C = -71. A < B2. A C3. (A < C) (B < C)

Boolean Operations: C++ A B A B A < B A > B A = B A B A B A B

A && B A | | B A < B A > B A = = B A > = B A < = B A < > B

Try this!Problem: You’d like to go see a movie. The movie costs $8.00, a soda costs

$2.50 and a large popcorn costs $4.50. Based on the amount of money in your

pocket, determine whether you could...(a) See the movie and buy a soda, (b) See the movie, and buy soda and popcorn, or(c) Stay home

Know?Movie costs $8.00Soda costs $2.50Popcorn costs $4.50How much money I have in my

pocket

Need?Cost of movie and sodaCost of movie, soda and popcornWay to select one of the three

options(that is, make a decision!)

Do?Option (a) costs $10.50Option (b) costs $15.00Option (c) costs nothingWhat next?

How about a diagram? This is

called a flowchart

Money < $15.00Stay home

Movie & sodaMovie, soda & popcorn

Money < $10.50

How about a diagram? Boxes

represent actions



Money < $10.50

How about a diagram? Diamonds

represent decision points



Money < $10.50

How about a diagram? Arrows

show flow



Money < $10.50

How about a diagram? The

arrow at the top tells us there were previous steps

The arrow at the bottom tells us there are subsequent steps



Money < $10.50

How would I write this?Using PseudocodeWait!What the CENSORED is

Pseudocode?

PseudocodeLooks like a programming

languageHas all the structure of a

programming languageHas a verrrrrry loose syntax

PseudocodeExample:

get xresult <- x2 + 5x + 7print result

That’s it!Sloppy, ain’t it?

One more time!Pseudocode...

If (Money < $10.50) thenStay homeelse If (Money < $15.00) then

Movie, sodaelse Movie, soda, popcorn

How would I write this?First, we need to decide how to

organize our solutionShould we “hard code” the costs of

the movie, soda and popcorn into the algorithm?

Should we input these values?Let’s take another look at that

problem!

How would I write this? The problem

statement tells us the individual costs

So, let’s assume they’re fixed or constant

No need to ask the user for them

Problem: You’d like to go see a movie. The movie costs $8.00, a soda

costs $2.50 and a large popcorn costs $4.50.

Based on the amount of money in your pocket, determine whether you could...(a) See the movie and buy a soda,(b) See the movie, and buy soda and popcorn, or(c) Stay home

How would I write this? Another question: Should we pre-

compute the cost of each option? Or, should we let the program do this? Since we’ve already stated that the

item costs are fixed, it would seem logical to pre-compute the cost of each optionMovie: $8.00Movie & soda: $10.50All three: $15.00

How would I write this?Next, we need to make sure we

have a complete algorithmInput MoneyIf (Money < $10.50) then

Display “Stay home.”else If (Money < $15.00) then

Display “Go to a movie;buy a soda.”else Display “Go to a movie; buy a

soda and popcorn.”

Almost done!

How would I write this?Determine how we wish to

organize our programDo we want one function?Or, should we create a few

functions?Let’s two functions: One to input Money from the user

And a second to determine the outcome

How would I write this?Here’s the prototypes for the

functions

int getMoney()

void showResults(int myMoney)

ProgramOkay, now we get to use our

algorithm and program design to create a program

Well, what are you waiting for?

Do It!!!

Multiway BranchingIf statements can be used for

multiway branchingThat is, choosing one of n mutually

exclusive outcomesBut what about n outcomes that

are not totally unique?

Multiway BranchingConsider the following problem:

Each year, a local middle school requires students to purchase supplies based on their grade level. 6th graders need pencils and five notebooks. 7th graders also need a calculator. 8th graders add to this a 3-ring binder with loose leaf paper.

Multiway Branching We could use a nested If statement to

handle this, but there is an alternative Whenever we need to represent a

decision step, with n possible outcomes, where the outcomes form subsets of each

other, and/orthe outcomes are chosen based upon

unique scalar values for a control expression,

we can use a Case (switch) structure

Multiway BranchingCase

When Grade = 8th3-ring binderloose leaf paper

When Grade = 7thcalculator

When Grade = 6thpencils5 notebooks

Multiway Branching In C++ ...switch (grade){

case 8:cout << “3-ring binder, loose leaf, “;

case 7:cout << “calculator, “;

case 6:cout << “5 notebooks, & pencils.” <<

endl;} When the switch is encountered, control jumps to the

matching case statement and continues until either a break is found or the end of the switch

Multiway BranchingHere’s an example with a few break’s

cout << “Your lunch period comes “;switch (grade) {

case 8:cout << “first.” << endl;break;

case 7:cout << “second.” << endl;break;

case 6:cout << “third.” << endl;

}

No final break

Exercise:Create a program that will inform

the user which advisor they should go to based on their major code number

Well? Get started!

LoopsComputer Science I

Q: What is a Loop?A control structure that allows for a

sequence of steps to be repeated a certain number of times

This sequence of steps is called the body of the loop

Q: What is a Loop?There are three basic loop

structures in programming:ForWhileRepeat

While loop

Condition

Body

T

F

Look familiar?

What if you added a change step to the end of the body?

For loop

Condition

Body

T

F

While loop

Condition

Body

T

F

A while loop is a control structure where the body is repeated as long as the condition is true

While loop

Condition

Body

T

F

When the condition is false, the body is bypassed, and flow continues with the next part of the algorithm

Example: Sequential search

k 0found Falsewhile (k<size) (found)

do if A[k] = target

then found True

else k = k + 1

(k<size) (found)

if A[k] = targetthen found Trueelse k = k + 1

T

F

Example: Sequential search

k = 0;

found = False;

while ((k<size) && (!found))

if (A[k] == target)

found = True;

else k = k + 1;

(k<size) (found)

if A[k] = targetthen found Trueelse k = k + 1

T

F

ExerciseStrings are arrays of charactersHow would you determine if a

string fragment is part of a larger string?(needle in a haystack?)

ArraysComputer Science I

Q: What is an array?An array is a data structure

consisting of one or more indexed members

An array is like a row of mailboxes at the post office

Each box is numbered in sequence (indices), and …

Each box contains the same type of stuff (datatype)

An array could be drawn like …

g d a f c z l

0 1 2 3 4 5 6


g d a f c z l

0 1 2 3 4 5 6

Each box is numbered in sequence


g d a f c z l

0 1 2 3 4 5 6

Each box has the same datatype

In pseudocode we use …X[j]Where X is the name of the array

(identifier), and …j is an index indicating which

position in the array we wish to address

An array is declared by …

int X[10]; Where int is the common datatype for

all elements in the array, X is the name of the array (identifier),

and … 10 is the size of the array, or how many

elements are in the array Indices for a C++ array always begin

with 0

Example: Student Grades

// Declare array

double stGrades[7];

:

// Assign value to array element

stGrades[5] = 87;

:

// Display array element

cout << stGrades[3] << endl;

Problem:Create a program that will ask the

user for three (3) numbers, determine the average, and then display the original numbers and the average

Hint: You might wish to use a loop as well as an array!

StringsComputer Science I

What is a string? A string is a sequence of characters Example:

nc9*hNB98B&^v*&G Blank spaces are characters Each character requires one byte of

storage in memory Each character is represented by a one

byte character code, usually an ASCII code

StringsA literal is a string bounded by

quotation marksExample:

“nc9*hNB 98B&^v*&G”Notice the blanks spaces in the

sequence - they are characters!

StringsIn C++, we declare string variables

as followschar string_identifier[length];

string_identifier is the name of the string variable

length represents the length of the string, or how many characters are in the sequence

StringsExample:

void main()

{

char name[24];

cout << “Enter your name: “;

cin >> name;

cout << “Your name is “ << name << endl;

}

Streams

A stream …Is a flow of charactersIs an object that represents either on

input or an output to a programCan be associated with the keyboard,

monitor, or files cout is an output stream cin is an input stream

How about file I/O?

#include <fstream.h>

:

ifstream in_stream;

ofstream out_stream;

:

Where definitions for datatypes ifstream and ofstream are located

Input stream declaration

Output stream declaration

How about file I/O?

#include <fstream.h>:ifstream in_stream;ofstream out_stream;:in_stream.open(“infile.txt”);out_stream.open(“outfile.txt”);instream >> number;outstream << number << endl;instream.close();outstream.close();:

Associates files with streams & opens files for use

Stream use

Closes files

What if a file doesn’t exist?

In_stream.open(“notthere.txt”);

If (in_stream.fail()){

cout << “Input file opening failed” << endl;

exit(1);}

How about formatting?

out_stream.setf(ios::fixed);

out_stream.setf(ios::showpoint);

out_stream.precision(2);

out_stream.width(10);

:

Set flag:

fixed/scientificshowpointshowposright/left

Number of decimal places

Number of digits

More member functionsget()put()eof()

Introduction to C++

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