Basic Notions Review

           what is a variable? value? address? memory location?

what is an identifier? variable name? keyword?

what is legal identifier? what identifiers are legal?

what are C-style, Pascal-style, Camel Back identifiers?

what is variable type? what types have we studied?

what is variable declaration? where (in the program) is a variable declaration placed?

what is an assignment?

what is a stream? input stream? output stream? cout? cin?

what is an extraction/insertion operator?

what is an escape sequence?

what is an input token?

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Types, Expressions, More on Assignment

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int , double and Others

type

is the kind of data that is stored in variables int - whole numbers double – numbers with fractions (called

floating point

) since the storage is limited, fraction can contain only a limited number of digits (usually up to 14) two ways to write a double number in C++  regular: 2.0 -3.23 +0.0456 .45

dot needs to be there  scientific or floating point (explicitly states

mantissa

and

exponent

)

:

5.89e5 .045E-4 5e+5 dot does not need to be there mantissa is limited in size. The largest allowable number differs for every architecture. Usually:  int - up to 32767  double - up to 10 308 int or double (or any other type in C++) cannot contain a comma other possible types are short , float and long double in this course, use int 3

Character Type

    a variable stores a single character, e.g. ’a’ , ’A’ , ’%’ , ’1’ declared char varName; note that ’1’ is also a character, not the same thing as numeric type 1 note also that ”1” is a string, not a character // asks for initials and outputs greeting #include main (){ char first, second; cout << ”Enter your initials: ”; cin >> first >> second; cout << ”Hello ” << first << second << endl; cout << ”pleased to meet you\n”; } 4

Type bool

   bool (short for boolean) is used for branching and looping statements a boolean variable can have only two values

true

or

false

bool result; result = true; true and false are keywords and cannot be used as identfiers 5

Literal Constants

    an explicitly stated value is a

literal constant

examples: 23 34.4 ’a’ true a literal constant has value and type what are the types of the above constants?

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Type Compatibility

     as a rule you cannot store a value of one type in a variable of another type trying to do it leads to

type mismatch

int intvar; intvar = 2.99; compiler prints this: warning: assignment to ’int' from ’double' but still compiles the program discarding the fractional part it is usually a bad idea (but some programmers do it) to store char values in variables of type int , bool s can also be in int . Even though you compiler allows it, it obscures the meaning of the variables and should be avoided 7

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Expressions

expression is a mechanism of calculating new values of objects from old ones; each expression (similar to variables and constants) has

type

and value simplest expression – literal constant with no operator applied; examples: 23 18.53

’a’ expression consists of

operands

and

operators arity -

 the number of operands the operator uses binary operator – two operands  unary operator – one operand 8

Binary Integer Operators

     addition subtraction Operator multiplication division remainder / * + % Example 2+3 count-2 a+4 ‘b’+1 4-7 5*6 12/3 width*height 4/5 10%3 23%4    for positive integers: if the integer division is not even, then the fractional part of the result is discarded: 12/5 produces 2 note that the fractional part is discarded and the result is never rounded up: 11/3 which should be (3.6666…) produces 3 not 4 the remainder can be used to “catch” the “missing” fraction 12%5 produces 2 9

Binary Double/Mixed Operators

    addition subtraction multiplication division Operator / * + Example 2.3 + 3.4

2.45 - 1.3

5.4*2.3

12.4 / 5.0

  there is no remainder operator with floating point if there are integer and floating-point operands then the integers are first converted (by compiler) to floating-point operands and then the expression is evaluated: 45.34 * 2 is converted to 45.34 * 2.0

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Unary Operators, Precedence

    unary operators are allowed: +23 -2.34

precedence

1. Unary + , (order of execution) follows mathematical conventions: 2. Binary * , / , % 3. Binary and + you can use () to change precedence: (2+3)*2 changes default precedence 2 / 3 + 5 -8 * 4 8 + 7 % 4 is equivalent to (2 / 3) + 5 (-8) * 4 8 + (7 % 4) 11

Whole Numbers in Division

   when you divide int by int the result is int . It may be problematic in expression and the problem is hard to spot the compiler would not complain this program converts feet into miles. Is there anything wrong with it?

double totalPrice; int feet; cin >> feet; totalPrice = 5000 * (feet/5280); 12

Assignment Conversions

   if double expression is assigned to an integer variable, its fractional part is dropped if int expression is assigned to a double converted to double variable, the expression is with zero fractional part consider double y = 2.7; int i = 15; int j = 10; i = y; // i is now 2 cout << i << endl; y = j; // y is now 10.0

cout << y << endl; 13

Compound Assignment

  C++ has a large set of operators for applying an operation to a variable and then writing the result back into the variable. Can be used for both int and double examples: int i = 3; i += 4; // equivalent to i=i+4; cout << i << endl;   double a = 3.2; a *= 2.0; // equivalent to a=a*2.0; cout << a << endl; examples of other compound assignments : time /= rush_factor; change %=100; amount *= cnt1+ cnt2; what is the equivalent of the last operator? 14

Increment and Decrement

    C++ has special operators for

incrementing

(increasing by one) or

decrementing

(decreasing by one) a variable value stored by a variable such operator can be used as a standalone statement ++k; or in an expression a = ++k + 5; operator have

prefix

and

postfix

(

suffix

) form   allowed in both standalone statements and expressions no difference in standalone statements (stylistic issue)  in expressions, – in prefix form, the operation applies before value used in expression int k=5; a = ++k+5; // a is 11, k is 6 – in suffix form, the operation applies after value is used in expression int k=5; a = k++ +5; // a is 10, k is 6 in modern programming postfix form is avoided: may be inefficient if complex types 15

Increment and Decrement Example

int k; k=4; ++k;

// k is 5

k++;

// k is 6

cout << k << endl; int i; i= k++;

// i is 6, k is 7

cout << i << " " << k << endl; int j; j= ++k;

// j is 8, k is 8

cout << j << " " << k << endl; 16

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Uninitialized Variables, Assignment at Declaration

any declared variable contains a value what is wrong with this program fragment?

int desiredNumber; desiredNumber=desiredNumber+5; to avoid uninitialized variable problem and make programs more concise C++ allows assignment at initialization: there are two allowed forms:  primary int count=0, limit=10; double distance=5.723, pi=3.14; double step=limit/2.0;  alternative int count(0), limit(10); double distance(5.723), pi(3.14); double step(limit/2.0); 17