Course A201: Introduction to Programming

1. Course A201:Introduction to Programming 09/09/2010

2. Recap [variable] • a name that carries/represents some value • You should give them values, before you use them because IDLE does not know what it is and what value it carries ex: service_rate = ‘good’ tip_percent = 0.15

3. Recap [types] integer • ex: 1; 3; 999; 8019 floating point (float) • ex: 0.8; 87.467; 3.14159 String • ex: “Hi”, “you name is: ”, “@$%^%$”

4. Recap [types] string: • consists of characters(letters, numbers, anything you can type in from keyboard) • always within single/double quotes • escape sequences: using back slash • ex: ‘good’; “Please enter: ”; ‘812000000’

5. Recap [types] string: • strings cannot be convert or compared to integers/floats unless they only contains numbers and are converted using type conversion functions • Ex: float(service) -> ERROR! Ex: ‘1’ == 1, result is False Ex: a = ‘1’;a + 2 -> ERROR!

6. Recap Type conversion functions: int(), str(), float() • Variables/Values on both side of “+”(concatenation) should be in the same type Ex: num1 = 2, num2 = 3 “Sum of ” + num2 + “ and ” + num2 -> ERROR! “Sum of ” + str(num2) + “ and ” + str(num2) • Be careful about logical errors

7. Recap [functions] • input1, input2, input3, … • You give me some inputs I am a function. I will perform a certain job. • I give you some outputs back, explicitly or implicitly • output1, output2, output3, …

8. Recap [functions: print] print: output things on the screen • Ex: date = ‘Sep. 23th’ print(‘Today is’,date) • All variables/values you put between parentheses are ARGUMENTS. (Important concept!!) Arguments are separated by comma -> , In the example above, you passes TWO arguments into the function print() • Here

9. Recap [functions: print] print(“Sum of ” + num2 + “ and ” + num2) -> ERROR! print(“Sum of ”,num2, “ and ”, num2) -> CORRECT! • In the first line, the concatenation will be executed first, that’s when error happens. Variables/values on both sides of + should be in the same type • In the second line, there are 3 commas. So, you actually passed 4 arguments into function print. Different arguments can be in different types.

10. Recap [functions: raw_input] raw_input: reads anything the user input from keyboard, and returns the value (store it in a variable you named) as a STRING • Ex: service_rate = raw_input(‘Please enter the service rate: ’) After this, no matter what the user entered, service_rate would be a string. • It is a prompt message

11. Recap [Arithmetic operations] • % : called modulo/modulus, returns remainder • / : division • // : floor division, returns the quotient • ** : exponent, 2**3 is 8 • Due to version conflict, the safest way to perform any division, convert the integers to floating numbers first. • a += 1 is short for a = a + 1

12. Have a nice weekend!