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

2. 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

3. 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

4. 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 is float

5. 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 = …
Cannot store with complete accuracy on computer!

6. Float Type and Memory
Python allocates limited number of digits for floats
Usually about 16 digits
1/3 = 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

7. 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
 1.23e-30
Why called “floating point” numbers

8. 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  y = 23 % 5  3

9. 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

10. 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

11. 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

12. Example: Celsius to Fahrenheit

13. 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

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

15. 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 …