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Chapter 3: Expressions and Interactivity

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Outline cin object Mathematical expressions Type Conversion and Some coding styles

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

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

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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

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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;

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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;

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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.

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Slide 3- 10

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Outline cin object Mathematical expressions Type Conversion and Some coding styles

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Slide 3- 12 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

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

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

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Example 7 * 10 - 5 % 3 * 4 + 9 means (7 * 10) - 5 % 3 * 4 + 9 70 - 5 % 3 * 4 + 9 70 - (5 % 3) * 4 + 9 70 - 2 * 4 + 9 70 - ( 2 * 4 ) + 9 70 - 8 + 9 ( 70 - 8 ) + 9 62 + 9 71

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Parentheses Parentheses can be used to change the usual order; expressions inside ( ) are evaluated first evaluate (7 * (10 - 5) % 3) * 4 + 9 ( 7 * 5 % 3 ) * 4 + 9 ( 35 % 3 ) * 4 + 9 2 * 4 + 9 8 + 9 17

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Slide 3- 17 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);

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

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Slide 3- 19 Algebraic Expressions

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

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Outline cin object Mathematical expressions Type Conversion and Some coding styles

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Slide 3- 23 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.

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

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Slide 3- 25 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 = 0.0675; const int NUM_STATES = 50;

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Slide 3- 26

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Slide 3- 27 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

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Slide 3- 28 Combined Assignment Look at the following statement: sum = sum + 1; This adds 1 to the variable sum.

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Slide 3- 29 Other Similar Statements

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Slide 3- 30 Other Similar Statements

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Slide 3- 31 Combined Assignment The combined assignment operators provide a shorthand for these types of statements. The statement sum = sum + 1; is equivalent to sum += 1;

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Slide 3- 32 Combined Assignment Operators

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Slide 3- 33 Combined Assignment Operators

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Slide 3- 34 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

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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

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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 9.261 cosine_value = cos(3.1415196/6); //Result is 0.866 Slide 3- 36

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