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Published byTommy Broadie Modified about 1 year ago

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Types and Arithmetic Operators CSIS 1595: Fundamentals of Programming and Problem Solving 1

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Data Types Each variable has specific type – numeric types (int and float) – strings – boolean (True or False) Define capabilities of variable – Numeric types manipulated with arithmetic operators – Strings manipulated with string functions – Booleans used in branching statements

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Dynamic Data Typing Based on current value stored in variable x = 3 x is an integer x = “Fred” x is now a string – Other languages (C, Java, etc.) require type to be set when variable declared and not later changed – Good idea to not change type in middle of program (confusing!) Can use type function to see current type of variable

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Numeric Data Types Two different numeric types – integer (whole numbers) – floating point (numbers with decimals) Based on type of literal assigned to variable – No decimal integer – Decimal float – Even if 0 after decimal 2.0 is float

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Numeric Data Types and Memory Numeric values must be stored in binary memory – No limit to size of integers in Python Other languages may limit to fixed storage size(64 bits, etc.) Problem: Some numbers may require infinite number of digits to store – Example: 1/3 = 0.3333333333333333333333… – Cannot store with complete accuracy on computer!

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Float Type and Memory Python allocates limited number of digits for floats – Usually about 16 digits 1/3 = 0.3333333333333333 in Python Affects accuracy of computation – 5 * 2/3 ≠ 2/3 * 5 Difference between integer and float numbers – integer arithmetic guaranteed to be accurate – float arithmetic not guaranteed

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Floats and Exponential Notation Exponential notation: digits e exponent – Equivalent to digits × 10 exponent Used to store arbitrarily large/small floats with limited number of digits – 0.0000000000000000000000000000123 1.23e-30 – Why called “floating point” numbers

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Arithmetic Operators Basic mathematical operators: + addition - subtraction Also have unary minus-number * multiplication / division ** exponentiation // quotient (like division but truncates result to integer) %remainder (what is left over after quotient) Example: x = 23 // 5 4 y = 23 % 5 3

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Arithmetic Operators and Types Result type based on operand type – integer op integer integer – float op float float – float op integer or integer op float float Exception: division – integer / integer float Even if the operands are divisible! If need to get a whole number, use // instead

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Explicit Type Conversion Can use type(value) to evaluate value as type x = float(3) 3.0 y = int(3.52) 3 Used to manually truncate to integer – Not same as rounding! Can convert strings to/from equivalent numbers s = str(3.52) ‘3.52’ x = float(“3.52”) 3.52 y = int(“3”) 3

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Parsing Input to Strings input function always returns a string – Even if user inputs a number Must convert to number before manipulating with arithmetic operators – Otherwise get runtime error Usual form: 1.Prompt for value (stored in string) 2.Use int or float to get correspond numeric value 3.Manipulate numeric value

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Example: Celsius to Fahrenheit

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Order of Evaluation x = 7 + 3 * 2 – Is this 20? Is this 13? – Depends on order of evaluation of operators Rules of operator precedence: – Exponentiation done first – Unary minus done next – Multiplicative operators (*, /, %, //) done next – Additive operators (+, -) done last – Operators at same level done left to right

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Parentheses and Precedence Can use parentheses to change order – Expression in parentheses evaluated before use in rest of expression x = (7 + 3) * 2 20

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Incremental Operators Many statements of form variable = variable op value – Variable changed in terms of current value Shortcut syntax: variable op= value Examples: x += 1 same as x = x + 1 x *= 2 same as x = x * 2 …

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