Fundamental Programming 310201 1 Fundamental Programming More Expressions and Data Types.

Fundamental Programming 310201 1

Fundamental Programming

More Expressions and Data Types


Status this week we continue to:

develop familiarity with the C++ language develop skill in software development (in lab) introduce fundamental programming concepts

last class we started to look at expressions they are important – they process the data we looked at numeric expressions and operators

today we look at another type of expression and learn a bit more about data types


Review of Expressions data processing occurs in expressions which

appear in assignment and output statements expressions exhibit the input-process-output

model: one or more inputs, one output operators transform input value(s) into an

output value - numeric operators: /, * , - , + rules control the order in which operators

are applied – e.g. multiplication & division before addition and subtraction


Pseudocode Examplewrite “Number of marks in exam ==> “ read NbrMarks write “Student’s mark ==> “read StudentMarkset Percentage to 100 * StudentMark / NbrMarkswrite “ Student’s percentage: “write Percentageif Percentage < 50 then write “ (Fail)”else write “ (Pass)”

numeric expression

operators

is this an operator?

is this an expression?


Truth-Valued Expressions yes, < is an operator - it’s a binary

operator< operand > < < operand >

and, yes, Percentage < 50 is an expression so, what is the value of this expression

- what does the expression evaluate to ? Answer: True or False (depending on value of Percentage)


Conditions in programming, truth-valued expressions

appear as the tests used to control selection (if-then-else) and repetition (while) statements

these tests are usually called conditions


Relational Operators less-than operator “<“ is one of a number of

operators we can use to compare two values other operators are: <=, =, >=, >, they are called relational operators in C++, not-equal is “!=“ also in C++, equality is “==“

if (ConversionType == 1)...

to distinguish from assignment operator ConversionType = 1;


Relational Operators in C++

a very common coding error is: if (ConversionType = 1)...

this code would not give a compilation error trap for young players - beware! more on this later…

no surprises with other relational operators in C++: <, <=, >=, >


More on Conditions consider the following logic…

if Percentage >= 65 and Percentage < 75 then write “ (Credit)”

is Percentage >= 65 and Percentage < 75 an expression?

is “and” an operator?


Boolean Operators yes, “and” is an operator - a binary operator and, yes, Percentage >= 65 and Percentage < 75 is an

expression - a truth-valued expression “or” is also a binary operator

if Percentage < 0 or Percentage > 100 then write “ Invalid Percentage!” “not” is a unary operator

if not Percentage >= 50 then write “ (Fail)” “and”, “or”, “not” called Boolean operators

- after Boole


Order of Use - General relational operators before Boolean operators

Percentage >= 65 and Percentage < 75 unary operator (not) before binary operators

(and & or) so, not Percentage >= 50 and Percentage > 0

is the same as: (not Percentage >= 50) and Percentage > 0

which is different from: not (Percentage >= 50 and Percentage > 0)


Order of Use – C++ in C++, truth-valued expressions must be enclosed in

parentheses the following gives a compilation error

if Percentage >= 50…

it must be:if (Percentage >= 50)…

instead of: if not Percentage >= 50 and Percentage > 0…

it’s… if ((not Percentage >= 50) and (Percentage > 0))…


Boolean Operators in C++ ANSI standard for C++ allows use of “and”, “or”, and

“not” in expressions in older compilers (like Turbo 4.5) use:

and: && or: || not: !

instead of: if ((not Percentage >= 50) and (Percentage > 0))…

it’s… if ((! Percentage >= 50) && (Percentage > 0))…


ActivityConsider the following expression: not Num1 Num2 or 4 / Num1 + Num2 > 5 The table below list combinations of values forNum1 and Num2. For each combination of values, show the value (True or False) of the expression.

Num1

Num2 not Num1 Num2 or 4 / Num1 + Num2 > 5

1 22 3


Activity Break


Activity FeedbackAlways clarify and simplify (if only in your mind): not Num1 Num2 or 4 / Num1 + Num2 > 5 (not Num1 Num2) or ((4 / Num1) + Num2 > 5) (Num1 = Num2) or ((4 / Num1) + Num2 > 5)

More activities like this in the Study Guide…

Num1

Num2 not Num1 Num2 or 4 / Num1 + Num2 > 5

1 2 True2 3 False


The Character Data Type in previous example programs, all values

assigned to variables have been numbers sometimes we wish to assign other types of

values to variables one other type of value we can assign to a

variable is a character – “a”, “b”, “c”, etc

an example to show how a character variable might be used is…


Character Variableswrite “Number of marks in exam ==> “ read NbrMarks set MoreMarks to “Y”while MoreMarks = “Y”

write “Student’s mark: “read StudentMark

set Percentage to 100 * StudentMark / NbrMarks write “ Student’s percentage: “ write Percentage

write “ Another mark ? [Y/N] ==> “read MoreMarks


in C++#include <iostream.h>void main (void){ int NbrMarks = 0; float StudentMark = 0, Percentage = 0;

char MoreMarks = ‘Y’; cout << "Number of marks in exam ==> "; cin >> NbrMarks;

while (MoreMarks == ‘Y’) { cout << "Student’s mark ==> "; cin >> StudentMark; Percentage = 100 * StudentMark / NbrMarks; cout << " Student’s percentage: "; cout << Percentage; cout << endl;

cout << “ Another mark ? [Y/N] ==> "; cin >> MoreMarks; }}

note: characters are enclosed in single quotes


The Boolean Data Type one other type of value we can assign to a

variable is a truth value – True or False how are True and False stored in a computer?

all data is stored as a string of 1s and 0s in C++, True is stored as 1, False as 0 try:

cout << (2 > 1);cout << (2 < 1);

an example to show how a Boolean variable might be used is…


Boolean Variableswrite “Number of marks in exam ==> “ read NbrMarks set MoreMarks to Truewhile MoreMarks

write “Student’s mark: “read StudentMark

set Percentage to 100 * StudentMark / NbrMarks write “ Student’s percentage: “ write Percentage

write “ Another mark ? [Y/N] ==> “read Replyif Reply = “N” then set MoreMarks to False

note: you may prefer to use while MoreMarks = True…


ANSI Standard C++#include <iostream.h>void main (void){

int NbrMarks = 0; float StudentMark = 0, Percentage = 0;

char Reply = ‘Y’; bool MoreMarks = true; cout << "Number of marks in exam ==> "; cin >> NbrMarks; while (MoreMarks) { cout << "Student’s mark ==> "; cin >> StudentMark; Percentage = 100 * StudentMark / NbrMarks; cout << " Student’s percentage: "; cout << Percentage; cout << endl; cout << “ Another mark ? [Y/N] ==> "; cin >> Reply; if (Reply == ‘N’) { MoreMarks = false; } }}

note: bool data type notsupported by old compilers

note: you may preferwhile (MoreMarks == true)…


Old C++ Compilers replace… :

int NbrMarks = 0; float StudentMark = 0, Percentage = 0;

char Reply = ‘Y’; bool MoreMarks = true; :

with… :

const true = 1, false = 0; int NbrMarks = 0; float StudentMark = 0,

Percentage = 0; char Reply = ‘Y’; int MoreMarks = true; :

note: constantsare similar to variables, but their value isfixed – not variable

note: use int instead of bool


Strings strings of characters are also important in

programming – e.g. names, student IDs, etc we will deal with strings in more detail later for now, the only place we will use a string is

when we output a message to the display cout << "Number of marks in exam ==> ";

note: strings are enclosed in double quotes characters are enclosed in single quotes


Code in C++ (for old compiler) set HiddenChar to “d”set AskAgain to Truewhile AskAgain

write “Guess the hidden character (0 to Exit) ==> “read Reply

if Reply = HiddenChar or Reply = “0” then set AskAgain to False if Reply = HiddenChar then write “Congratulations!”


A Start#include <iostream.h>void main (void){ const true = 1,

false = 0; char HiddenChar = 'd', Reply = ' '; int AskAgain = true;

}


Activity Break


A Solution #include <iostream.h>void main (void){ const true = 1,

false = 0; char HiddenChar = 'd', Reply = ' '; int AskAgain = true;

while (AskAgain) {

cout << "Guess the hidden character (0 to Exit) ==> "; cin >> Reply; if ((Reply == HiddenChar) || (Reply == '0')) { AskAgain = false; if (Reply == HiddenChar) { cout << "Congratulations!"; }

} }}


Summary of Concepts expressions used in:

assignment statements output statements conditions (selection and repetition statements)

operators in numeric expressions : +, -, *, / operators in truth-valued expressions :

relational : <, <=, =, >=, >, Boolean : and, or, not

we now have four types of data: numbers, characters, Boolean, strings


C++ Syntax Summary input : cin >> <variable>; output : cout << <expression>; assignment : <variable> = <expression>; a selection statement:

if ( <condition> ){ <if-block statements> }

else{ <else-block statements> }

a repetition statement: while ( <condition> ){ <while-block statements> }


C++ Syntax Summary data types declared as:

numbers – int or float characters – char Boolean – bool strings left to later

in C++: truth-valued expression enclosed in parentheses equality operator is “ ==“ not-equal operator is “ !=“ characters enclosed in single quotes strings enclosed in double quotes True is 1, False is 0


C++ Syntax for Old Compilers use &&, ||, ! for “and”, “or”, and “not” in place of bool, use int variables, with

constants true (1) and false (0)

Fundamental Programming 310201 1 Fundamental Programming More Expressions and Data Types.

Documents

Transcript of Fundamental Programming 310201 1 Fundamental Programming More Expressions and Data Types.