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

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

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

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

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!

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

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

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

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

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

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: Prompt for value (stored in string) Use int or float to get correspond numeric value Manipulate numeric value

Example: Celsius to Fahrenheit

Order of Evaluation x = 7 + 3 * 2 Rules of operator precedence: 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

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

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 …