Chapter 3: Expressions and Interactivity

Outline cin object Mathematical expressions Type Conversion and Some coding styles

The cin Object Standard input object Like cout, requires iostream file Used to read input from keyboard

How to use cin ? SYNTAX These examples yield the same result. cin >> length ; cin >> width ; or cin >> length >> width ; cin >> Variable >> Variable... ;

The cin Object Information retrieved from cin with >> (the extraction operator) – operator >> attempts to extract the next item from the input stream and store its value in the right operand variable Input is stored in one or more variables

Slide 3- 7 The cin Object cin converts data to the type that matches the variable: int height; cout << "How tall is the room? "; cin >> height;

Slide 3- 8 Displaying a Prompt A prompt is a message that instructs the user to enter data. You should always use cout to display a prompt before each cin statement. cout > height;

Slide 3- 9 The cin Object Can be used to input more than one value: cin >> height >> width; Multiple values from keyboard must be separated by spaces Order is important: first value entered goes to first variable, etc.

Slide 3- 10

Outline cin object Mathematical expressions Type Conversion and Some coding styles

Slide Mathematical Expressions Can create complex expressions using multiple mathematical operators An expression can be a literal, a variable, or a mathematical combination of constants and variables

Mathematical Expressions Can be used in assignment, cout, other statements: area = 2 * PI * radius; cout << "border is: " << 2*(l+w);

Some C++ operators Precedence Operator Description Higher +Positive - Negative * Multiplication / Division %Modulus Addition - Subtraction Lower = Assignment

Example 7 * % 3 * means (7 * 10) - 5 % 3 * % 3 * (5 % 3) * * ( 2 * 4 ) ( )

Parentheses Parentheses can be used to change the usual order; expressions inside ( ) are evaluated first evaluate (7 * (10 - 5) % 3) * ( 7 * 5 % 3 ) * ( 35 % 3 ) * *

Slide Algebraic Expressions Multiplication requires an operator: Area=lw is written as Area = l * w; Parentheses may be needed to maintain order of operations: is written as m = (y2-y1) /(x2-x1);

When calculation average Average = a + b + c / 3.0; (Wrong!!!) Average = (a + b + c) / 3.0; (Correct!!!)

Slide Algebraic Expressions

Algebra and C++ expressions y = 3 * x /2; A = (3*x+2)/(4*a-1); d = b*b -4*a*c;

Outline cin object Mathematical expressions Type Conversion and Some coding styles

Slide When You Mix Apples and Oranges: Type Conversion Operations are performed between operands of the same type. If not of the same type, C++ will convert one to be the type of the other This can impact the results of calculations.

Example double parts; parts = 15/6;//parts=2 double parts; parts = 15.0/6;//parts=2.5

Slide Named (Symbolic) Constants Named constant (constant variable): variable whose content cannot be changed during program execution Often named in uppercase letters Used for representing constant values with descriptive names: const double TAX_RATE = ; const int NUM_STATES = 50;

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Slide Multiple Assignment and Combined Assignment The = can be used to assign a value to multiple variables: x = y = z = 5; Value of = is the value that is assigned Associates right to left: x = (y = (z = 5)); value is 5 value is 5 value is 5

Slide Combined Assignment Look at the following statement: sum = sum + 1; This adds 1 to the variable sum.

Slide Other Similar Statements

Slide Other Similar Statements

Slide Combined Assignment The combined assignment operators provide a shorthand for these types of statements. The statement sum = sum + 1; is equivalent to sum += 1;

Slide Combined Assignment Operators

Slide Combined Assignment Operators

Slide Mathematical Library Functions #include Commonly used functions: where n can be an integer, double, float. sin(n) Sine cos(n) Cosine tan(n) Tangent sqrt(n) Square root log(n) Natural (e) log abs(n) pow(b,n) Absolute value (takes and returns an int) Exponents

Mathematical Library Functions In order to user the functions you need to know: name of the function you need what the function does (input/output) input parameter and the data type of parameter data type of returned value Syntax: value = function_name (argument); Slide 3- 35

Mathematical Library Functions Examples: sqrt_value = sqrt(49);//Result is 7 abs_value = abs(-34.5);//Result is 34.5 power_value = pow(2.1,3);//Result is cosine_value = cos( /6); //Result is Slide 3- 36