3 3 Recap Variables and Data types Functions Control Structures.

33Recap

Variables and Data typesFunctions

Control Structures

RECAP Wrote our first program in C++.

1 // Fig. 2.1: fig02_01.cpp

2 // Text-printing program.

3 #include <iostream> // allows program to output data to the screen

4

5 // function main begins program execution

6 int main()

7 {

8 std::cout << "Welcome to C++!\n"; // display message

9

10 return 0; // indicate that program ended successfully

11

12 } // end function main

Welcome to C++!

Function main part of every program

Body delimited by {}

Multiple ways to write comments in code

Writing Simple output statements using stream insertion

operator <<

Function main returning 0,

execution ends here

Begin with appropriate

include statements

Escape Characters, preceded by ‘\’

indicates special character output

Statements instruct a program to perform actionAll statements end with a

semicolon

Fig. 2.2 | Escape sequences.

Escape sequence

Description

\n Newline. Position the screen cursor to the beginning of the next line.

\t Horizontal tab. Move the screen cursor to the next tab stop.

\r Carriage return. Position the screen cursor to the beginning of the current line; do not advance to the next line.

\a Alert. Sound the system bell.

\\ Backslash. Used to print a backslash character.

\' Single quote. Use to print a single quote character.

\" Double quote. Used to print a double quote character.

Outline

fig02_03.cpp

(1 of 1)

fig02_03.cpp output (1 of 1)

1 // Fig. 2.3: fig02_03.cpp

2 // Printing a line of text with multiple statements.


4


6 int main()

7 {

8 std::cout << "Welcome ";

9 std::cout << "to C++!\n";

10


12


Welcome to C++!

Multiple stream insertion statements produce one line of output

Outline

fig02_04.cpp

(1 of 1)


1 // Fig. 2.4: fig02_04.cpp

2 // Printing multiple lines of text with a single statement.


4


6 int main()

7 {

8 std::cout << "Welcome\nto\n\nC++!\n";

9


11


Welcome to C++!

Use newline characters to print on multiple lines

RECAP

• Syntax errors– A syntax error occurs when the compiler encounters code

that violates C++’s language rules (i.e., its syntax). The compiler normally issues an error message to help the programmer locate and fix the incorrect code.

– C++ case sensitive

– Semicolon after each statement

– Syntax errors encountered in lab

1 // Fig. 2.5: fig02_05.cpp

2 // Addition program that displays the sum of two numbers.

3 #include <iostream> // allows program to perform input and output

4


6 int main()

7 {

8 // variable declarations

9 int number1; // first integer to add

10 int number2; // second integer to add

11 int sum; // sum of number1 and number2

12

13 std::cout << "Enter first integer: "; // prompt user for data

14 std::cin >> number1; // read first integer from user into number1

15

16 std::cout << "Enter second integer: "; // prompt user for data

17 std::cin >> number2; // read second integer from user into number2

18

19 sum = number1 + number2; // add the numbers; store result in sum

20

21 std::cout << "Sum is " << sum << std::endl; // display sum; end line

22


24

25 } // end function main Enter first integer: 45 Enter second integer: 72 Sum is 117

How to Declare integer variables• Can declare several of them on one line, comma separated• Variable names can be any valid identifier, which is not a keyword• Series of characters (letters, digits, underscores)

• Cannot begin with digit

Use stream extraction operator with standard input stream to obtain user input• Input stream object

std::cin from <iostream>• Usually connected to keyboard• Stream extraction operator >>

• Waits for user to input value, press Enter (Return) key• Stores value in variable to right of operator

• Converts value to variable data typeConcatenating, chaining or cascading

stream insertion operations

Assignment operator =• Assigns value on left to variable on right

• Binary operator (two operands)• Add the values of variable1 and variable2• Store result in sum

Recap Variables and Memory

• Variable names– Correspond to actual locations in computer's memory

• Every variable has name, type, size and value

– When new value placed into variable, overwrites old value• Writing to memory is destructive

– Reading variables from memory nondestructive– Example

• sum = number1 + number2;– Value of sum is overwritten– Values of number1 and number2 remain intact

Memory locations after calculating and storing the sum of number1 and number2.

Recap Arithmetic

•Arithmetic operators–*

•Multiplication –/

•Division•Integer division truncates remainder

–7 / 5 evaluates to 1–%

•Modulus operator returns remainder –7 % 5 evaluates to 2

C++ operation C++ arithmetic operator

Algebraic expression

C++ expression

Addition + f + 7 f + 7

Subtraction - p – c p - c

Multiplication * bm or b· m b * m

Division / x / y or x

y or x ÷ y x / y

Modulus % r mod s r % s

Recap Arithmetic (Cont.)•Rules of operator precedence

–Operators in parentheses evaluated first•Nested/embedded parentheses

–Operators in innermost pair first

–Multiplication, division, modulus applied next•Operators applied from left to right

–Addition, subtraction applied last•Operators applied from left to right

Operator(s) Operation(s) Order of evaluation (precedence)

( ) Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

*

/

%

Multiplication

Division

Modulus

Evaluated second. If there are several, they are evaluated left to right.

+ -

Addition

Subtraction Evaluated last. If there are several, they are evaluated left to right.

Recap: Decision Making

• Condition– Expression can be either true or false

– Can be formed using equality or relational operators

•if statement– Guards a block of statements

– If condition is true, body of the if statement executes

– If condition is false, body of the if statement does not execute

• ………..

• statement0;

• if ( condition )

• statement1;

• statement2;

• ……………..

Recap: Decision Making

Recap: Decision Making• Condition

– Expression can be either true or false

– Can be formed using equality or relational operators

• if statement– If condition is true, body of the if statement executes

– If condition is false, body of the if statement does not execute• if ( condition )

• {

• }

Fig. 2.12 | Equality and relational operators.

Standard algebraic equality or relational operator

C++ equality or relational operator

Sample C++ condition

Meaning of C++ condition

Relational operators

> x > y x is greater than y

< x < y x is less than y

>= x >= y x is greater than or equal to y

<= x <= y x is less than or equal to y

Equality operators

= == x == y x is equal to y

≠ != x != y x is not equal to y

1 // Fig. 2.13: fig02_13.cpp

2 // Comparing integers using if statements, relational operators

3 // and equality operators.

4 #include <iostream> // allows program to perform input and output

5

6 using std::cout; // program uses cout

7 using std::cin; // program uses cin

8 using std::endl; // program uses endl

9


11 int main()

12 {

13 int number1; // first integer to compare

14 int number2; // second integer to compare

15

16 cout << "Enter two integers to compare: "; // prompt user for data

17 cin >> number1 >> number2; // read two integers from user

18

19 if ( number1 == number2 )

20 cout << number1 << " == " << number2 << endl;

21

22 if ( number1 != number2 )

23 cout << number1 << " != " << number2 << endl;

24

25 if ( number1 < number2 )

26 cout << number1 << " < " << number2 << endl;

27

28 if ( number1 > number2 )

29 cout << number1 << " > " << number2 << endl;

30

using declarations eliminate need for std:: prefix

Can write cout and cin without std:: prefix

Declare variables

if statement compares values of number1 and number2 to test for equality

If condition is true (i.e., values are equal), execute this statementif statement compares values

of number1 and number2 to test for inequality

If condition is true (i.e., values are not equal), execute this statement

Compares two numbers using relational operator < and >

Outline

fig02_13.cpp

(2 of 2)


(2 of 3)

(3 of 3)

31 if ( number1 <= number2 )

32 cout << number1 << " <= " << number2 << endl;

33

34 if ( number1 >= number2 )

35 cout << number1 << " >= " << number2 << endl;

36


38

39 } // end function main Enter two integers to compare: 3 7 3 != 7 3 < 7 3 <= 7 Enter two integers to compare: 22 12 22 != 12 22 > 12 22 >= 12 Enter two integers to compare: 7 7 7 == 7 7 <= 7 7 >= 7

Compares two numbers using relational operators <= and >=

Details of relational operatorsRelational (comparison) operators work as expected with int and double values, what about string and bool?

23 < 45 49.0 >= 7*7 "apple" < "berry"

Strings are compared alphabetically so that "ant" < "zebra" but (suprisingly?) "Ant" < "zebra"

How do lengths of strings compare?

Why does uppercase ‘A’ come before lowercase ‘z’?

Boolean values have numeric equivalents, 1 is true, 0 is false

cout << (23 < 45) << endl;

cout << ("guava" == "Guava") << endl;

Details of relational operators

• What about true/false and numeric one/zero equivalent? if (3 + 4 – 7) { cout << "hi" << endl; }• Boolean expressions can be combined using logical operators: AND, OR, NOT C++ equivalents are &&, ||, and !, respectively

(standard requires and, or, not, most compilers don’t)

if (90 <= grade) {

if (grade < 95) {

cout << "that’s an A" << endl;}

}• What range of values generates ‘A’ message? Problems?

if (90 < grade && grade < 95) {

cout << "that’s an A" << endl; }

Write a program that prompts the user for a number in seconds and then determines how many hours, minutes and seconds does this represent

Example:Please Enter the number of seconds: 2000The number you entered represents5 Hours, 33 Minutes and 20 Seconds.

Using If statements, Only display hours and minutes if you have to. If the input number is less than an hour, only display minutes and seconds.

Example:Please Enter the number of seconds: 200The number you entered represents3 Minutes and 20 Seconds.

If input number is less than a minute, the answer should only display seconds

Example:Please Enter the number of seconds: 20The number you entered represents20 Seconds.

Variables and Data types

• Variable names– Correspond to actual locations in computer's memory

• Every variable has name, type, size and value

• Memory in computers is organized in bytes

• A byte is the minimum memory we can manage in C++

• A Byte can store one single character or small integer

• More complex data types come from grouping several bytes

• The size and ranges of data types is dependent on the system the program is compiled for

• Basic Fundamental Data types in C++

If Else statement• #include <iostream>• #include <string>• using namespace std;• // illustrates use of if-else statement• int main()• { • string response; • cout << "Do you like broccoli [yes/no]> "; • cin >> response; • if ("yes" == response) • { • cout << "Green vegetables are good for you" << endl; • cout << "Broccoli is good in stir-fry as well" << endl; • } • else • { • cout << "(There is no accounting for taste)" << endl; • } • return 0;• }

If Else statement• if (condition) statement1 else statement2• The if + else structures can be concatenated with the intention of verifying a range of values

• if (x > 0) • cout << "x is positive"; • else if (x < 0) • cout << "x is negative"; • else cout << "x is 0";

Nested If Else

• Nested if…else statements– One inside another, test for multiple cases – Once a condition met, other statements are skipped– Example

• If student’s grade is greater than or equal to 90– Print “A”– Else

If student’s grade is greater than or equal to 80 Print “B”

Else If student’s grade is greater than or equal to 70

Print “C” Else If student’s grade is greater than or equal to 60 Print “D”

Else• Print “F”

Nested If Else

• Nested if…else statements (Cont.)

– Written In C++

• if ( studentGrade >= 90 ) cout << "A";else if (studentGrade >= 80 ) cout << "B"; else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D"; else cout << "F";

• A nested if...else statement can perform much faster than a series of single-selection if statements because of the possibility of early exit after one of the conditions is satisfied.

Nested If Else

• Dangling-else problem– Compiler associates else with the immediately

preceding if– Example

• if ( x > 5 ) if ( y > 5 ) cout << "x and y are > 5";else cout << "x is <= 5";

– Compiler interprets as• if ( x > 5 ) if ( y > 5 ) cout << "x and y are > 5"; else cout << "x is <= 5";

Nested If Else

• Dangling-else problem (Cont.)– Rewrite with braces ({})

• if ( x > 5 ){ if ( y > 5 ) cout << "x and y are > 5";}else cout << "x is <= 5";

– Braces indicate that the second if statement is in the body of the first and the else is associated with the first if statement

Compound Statement

• Compound statement– Also called a block

• Set of statements within a pair of braces• Used to include multiple statements in an if body

– Example• if ( studentGrade >= 60 )

cout << "Passed.\n";else { cout << "Failed.\n"; cout << "You must take this course again.\n";}

– Without braces,– cout << "You must take this course again.\n";

– always executes• A block can be placed anywhere in a program that a single statement can be

placed.

Good Programming practice

• Always putting the braces in an if...else statement (or any control statement) helps prevent their accidental omission, especially when adding statements to an if or else clause at a later time. To avoid omitting one or both of the braces, some programmers prefer to type the beginning and ending braces of blocks even before typing the individual statements within the braces.

Variables and Data typesName Description Size* Range*

char Character or small integer. 1byte signed: -128 to 127 unsigned: 0 to 255

short int (short) Short Integer. 2bytes

signed: -32768 to 32767 unsigned: 0 to 65535

int Integer. 4bytes signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295

long int (long) Long integer. 4bytes

signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295

bool Boolean value. I t can take one of two values: true or false.

1byte true or false

float Floating point number. 4bytes +/- 3.4e +/- 38 (~7 digits)

double Double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)

long double Long double precision floating point number.

8bytes +/- 1.7e +/- 308 (~15 digits)

Declaration of Variables

• Declare variables by specifying type• Followed by identifier or name of variable

• • integer datatypes char, short, int can either be signed or unsigned• if not specified, default is signed• signed types can represent both +ve and –ve numbers• Unsigned types can only represent +ve values or 0

int a;

float mynumber;

int c, d , e;

unsigned short int NumberOfsisters;

signed int myaccountbalance;

Declaration of Variables

• short and long can be used alone as type specifiers• In that case, they refer to their integer fundamental types

• signed and unsigned can be used similarly

short year;

short int Year;

unsigned NextYear;

unsigned int NextYear;

Scope of Variables

• Variables must be declared before use• Variable can either be local or global scope• Global variables can be referred from anywhere

in the code • Scope of local variables is limited by the block {}

in which they are declared• For example if they are declared at the beginning

of the body of a function their scope is limited to the end of the function

Scope of Variables

#include <iostream>using namespace std;void test () { int a=5; cout << “Value of ‘a’ in test =”<<a;}

int main (){ int a=10; cout << “Value of ‘a’ in main=”<<a<<endl; test(); return 0;}

Scope of Variables

Run:

SCOPE.exe

Initialization of Variables

• value of a local variable is undetermined by default

• can be given a value using assignment operator

• int a = 10;• constructor initialization can also be used• int a (0);• both ways are equivalent

Constants

• constants are expressions with fixed value

• Literal constants are used to express particular values within the source code of a program

• Literals can be Integer Numerals, Floating point numerals, Characters, Strings and boolean values

• Integers can be decimal, octal or hex• char enclosed in single quotes ‘’• strings enclosed in “”

75 // decimal;

0113 // Octal;

0x4b // hex;

75u // unsigned int;

75l // long;

3.14159 // 3.14159

6.02e23 // 6.02 x 10^23

1.6e-19 // 1.6 x 10^-19

3.0 // 3.0

'z' // character ‘z’

'p' // character ‘p’

"Hello world"

Constants

• can define own names for constants without memory consuming variable// defined constants: calculate circumference

#include <iostream>using namespace std;

#define PI 3.14159#define NEWLINE '\n'

int main (){ double r=5.0; // radius double circle; circle = 2 * PI * r; cout << circle; cout << NEWLINE; return 0;}

Constants

• const prefix can declare variables whose values cannot be modified once they are defined

const int pathwidth = 100; const char tabulator = '\t';

Strings

• Introduced in the lab• inherit from the string class• non-numerical values longer than one

character– example: string name, password;– can be initialized with any valid string literal

// my first string

#include <iostream>

#include <string>

using namespace std;

int main ()

{

string mystring;

mystring = "This is the initial string content";

cout << mystring << endl;

mystring = "This is a different string content";

cout << mystring << endl;

return 0;

}

Strings

Towards functions (Face1)

#include <iostream>


int main()

{

cout << " |||||||||||||||| " << endl;

cout << " | | " << endl;

cout << " | o o | " << endl;

cout << " _| |_ " << endl;

cout << "|_ _|" << endl;

cout << " | |______| | " << endl;

cout << " | | " << endl;

return 0;

}• Prints head, but not as modular as program using functions

– Harder to modify to draw differently

Introduction to Functions (Face2)#include <iostream>


// print a head, use of functions

void Head ()

{ cout << “ ////////|\\\\\\\\ “ << endl;cout << “ | | “ << endl;cout << “ | o o | “ << endl;cout << “ _| O |_ “ << endl;cout << “ |_| “=” |_| “ << endl;cout << “ | |_______| | “ << endl;cout << “ | | “ << endl;cout << “ | | “ << endl;cout << “ |---------------| “ << endl;

}

int main (){ Head (); return 0;}

Introduction to Functions#include <iostream>using namespace std;void Hair(){

cout << “ ////////|\\\\\\\\ “ << endl;}void side(){

cout << “ | | “ << endl;}void eyes(){

cout << “ | o o | “ << endl;}void nose(){

cout << “ _| O |_ “ << endl;}void moustache(){

cout << “ |_| “=” |_| “ << endl;}void mouth(){

cout << “ | |_______| | “ << endl;}void chin(){

cout << “ |---------------| “ << endl;}

Introduction to Functionsvoid Head(){

Hair();side{};eyes();nose();moustache();mouth();side();side();chin();

}int main(){ Head (); return 0;}

Function with parameters

• Using a calculator √100• 100 is the argument of the square root

function• Functions that take arguments are called

parameterized functions• Parameters are useful in making functions

more general• Functions that receive parameters must

receive the correct parameters

Happy Birthday#include <iostream>using namespace std;#include <string>

void Sing(string person){

cout << “ Happy Birthday to you ” << endl;cout << “ Happy Birthday to you ” << endl;cout << “ Happy Birthday dear ”<< person << endl;cout << “ Happy Birthday to you ” << endl;cout << endl;

}int main(){ Sing ( “Alice”); Sing ( “John”); Sing ( “Alan”); return 0;}

Happy Birthday• When Sing (“Alice”) is called when main is executed, Alice is passed to the function as ‘person’

• when cout << “ Happy Birthday” << person <<endl; is executed, person is replaced by ‘Alice’

• Each parameter passed to a function has a name and a type

• Functions can have several parameters

• Example int Addition (int x, int y), called as Addition (2,3)

• Will study passing arguments to functions in detail later

• What if we do Sing(1234)?

• Compiling...

• HappyBirthday.cpp

• C:\Program Files\Microsoft Visual Studio\MyProjects\HappyBirthday\HappyBirthday.cpp(23) : error C2664: 'Sing' : cannot convert parameter 1 from 'const int' to 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >'

• No constructor could take the source type, or constructor overload resolution was ambiguous

• Error executing cl.exe.

• HappyBirthday.exe - 1 error(s), 0 warning(s)

Function prototype• Functions have prototypes (or signatures) that indicate to both the compiler and the

programmer how to use the function– Later functions will return values, like square root

– For now, void means no value is returned

– Every function has a parameter list, but it’s possible to have no parameters• Hello(); colorOfAnimal(“crow”,”black”);

• What do prototypes look like for these calls?

• Cant use variables before they are defined

• Can use functions before they are defined – How?

– Add function prototype before the function is called

– The prototype shows the order and type of arguments for the function as well as return type

– Example?

Function prototype// order.cpp : Defines the entry point for the console application.//#include "stdafx.h"#include <iostream>#include <string>using namespace std;

// order of procedures is important

void Hi (string name){ cout << "Hi " << name << endl; Greetings();}

void Greetings(){ cout << "Things are happening inside this computer" << endl;}

int main(){ Hi("Fred"); return 0;}

Function prototypeCompiling...StdAfx.cppCompiling...order.cppC:\Program Files\Microsoft Visual Studio\MyProjects\order\order.cpp(15) : error C2065: 'Greetings' : undeclared identifierC:\Program Files\Microsoft Visual Studio\MyProjects\order\order.cpp(19) : error C2373: 'Greetings' : redefinition; different type modifiersError executing cl.exe.

order.exe - 2 error(s), 0 warning(s)

Function prototype#include "stdafx.h"#include <iostream>#include <string>using namespace std;

// illustrates function prototypesvoid Hi(string);void Greetings();

void Hi (string name){ cout << "Hi " << name << endl; Greetings();}

void Greetings(){ cout << "Things are happening inside this computer" << endl;}

int main(){ Hi("Fred"); return 0;}

Operators• Operators to operate on variables and constants• Assignment operator =• Arithmetic operators

– +, -, *, /, %• Compound assignment

– +=, -=, *=, /=, %=– Value += increase Value = Value + increase– Value -= increase Value = Value - increase– Value *= increase Value = Value * increase– Value /= increase Value = Value / increase– Value %= increase Value = Value % increase

• Increase / Decrease– ++ --– C++;– C+=1;– C=C+1– Can be used both as prefix or suffix– Prefix is evaluated before result of expression is evaluated– Suffix is evaluated after expression is evaluated

Operators• B= 3;

• A= ++B;

• //A now contains 4, B contains 4

• B = 3;

• A= B++;

• //A contains 3, B contains 4

• In the first scenario, B is increased before value is assigned to A

• In the second scenario, B is increased after the value is assigned to A

Operators• Relational and Equality Operators

– == Equal to

– != Not equal to

– > Greater than

– < Less than

– >= Greater than or equal to

– <= Less than or equal to• Logical Operators

– !, &&, ||

• Type casting operators

– int I;

– float F = 3.14;

– I = (int) F;

While Loops

• // custom countdown using while

• #include <iostream>• using namespace std;

• int main ()• {• int n;• cout << "Enter the starting number > ";• cin >> n;

• while (n>0) {• cout << n << ", ";• --n;• }

• cout << "FIRE!\n";• return 0;• }

• Enter the starting number > 8 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

3 3 Recap Variables and Data types Functions Control Structures.

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Transcript of 3 3 Recap Variables and Data types Functions Control Structures.