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Computer Science 1MD3

Introduction to Programming

Winter 2014

About the questions

I would like to answer your questions about python which you cannot understand well or some programs questions related to 1MD3.

You can ask me your questions about the assignments, for example, you cannot understand the assignment questions themselves, or if you need some help when you are doing the python programs.

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Email me and describe your questions in your email and I will reply to you as soon as possible when I read your email. But you need describe your questions clearly. Gmail Chat ？ Maybe Not a good way to explain program……

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My email: fumq@mcmaster.ca or mingquanfubonsoir@gmail.com

My office: ITB 206

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Assignment 1

Due date: by Thu. Jan 30 23:00:00 2014

Assignment 2

Due date: by Wed Feb 26 23:00:00 2014

Introduction

Syntax and semantics of programming language

Syntax and semantics of python Assignment statements Conditional statements Loop statements Function

Exception (related to file I/O and object)

Assignment: Main points of Assignment 1 Main points of Assignment 2

Language and programming language

Language: [1]Language provides a means of communication by sound and writtensymbols. Human beings learn language as a consequence of their lifeexperiences.

Natural language:[1] We communicate our thoughts and feelings Sometimes, it’s not very exactly in using science

Programming language:[1] Can be viewed as artificial languages defined by men and women

initially for the purpose of communicating with computers but, as importantly, for communicating algorithms among people.

Syntax of programming language

Syntax refers to the ways symbols may be combined to create well-formed sentences (or programs) in the language. [1]

Syntax defines the formal relations between the constituents of a language, thereby providing a structural description of the various expressions that make up legal strings in the language. [1]

Syntax deals solely with the form and structure of symbols in a language without any consideration given to their meaning.[1]

Semantics of programming language

Semantics reveals the meaning of syntactically valid strings in a language.[1]

For natural languages, this means correlating sentences and phrases with the objects, thoughts, and feelings of our experiences. [1]

For programming languages, semantics describes the behavior that a computer follows when executing a program in the language. [1]

We might disclose this behavior by describing the relationship between the input and output of a program or by a step-by-step explanation of how a program will execute on a real or an abstract machine. [1]

Program

Program: A computer program, or just a program, is a sequence

of instructions, written to perform a specified task with a computer. [2]

Software: A collection of computer programs and related data is

referred to as the software. [2]

Math + logic + English (we need algorithms in programs)

www.michaelliut.ca/cs1md3

Programming Languages

How many programming Languages exists?

Parts of them are here:

http://en.wikipedia.org/wiki/List_of_programming_languages

You may know or will study in future:

C, Java, C++, Haskell, Ruby, Pascal, Visual Basic, Object Pascal(Delphi), …

If Statements

Boolean Boolean value: true or false Boolean expression

if condition: print (……) elif condition: print (……) else

left associative : 5**2 **3 = (5**2)**3 Right associative Elif a+b+c ==a+b

If Statements

This Flow Diagram is taken from [3]

If statement

If examples

i1 = 1if i1: print("i1 if branch")else: print ("i1 else branch")i2 = 0if i2: print ("i2 if branch") else: print ("i2 else branch") print ("finish the program")

Main points of assignment1

If..elif If a o b o c == (a o b) o c left associative If a o b o c == a o (b o c) right associative

We need “import calendar” from Eval (input(“”) to get the input year By calendar.month(year, month) to get the

month calendar

• This Flow Diagram is taken from [3]

Loop

Loop

Loop Type Description[3]

while loop

Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.

for loop

Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.

nested loopsYou can use one or more loop inside any another while, for or do..while loop.

While Loop

This Flow Diagram is taken from [3]

While Loop

While example

i=3while i>0: print("this is a positive number") print(i) i=i-1print("finish the while loop, i equal to 0 now")print(i)

For Loop

This Flow Diagram is taken from [3]

For Loop

for example

for i in range(3, 0, -1):

print("this is a positive number") print(i) print("finish the while loop")print(i)

Main points of assignment1

Using while loop or for loop

% modulo operator: find the division remainder of a number

s =s + v

Function

Why do we need functions in python?

Syntax of function

.

Function

Function syntax

Syntax:def name( parameters ): function_body return [expression]

Function

The example adapted from [3]

Function definition and call

def appendlist( l ): l.append(4); return

# call functionl = [1,2,3];appendlist( l );print (l)

Exception

What is Exception? An exception is an event, which occurs during the execution of a program,

that disrupts the normal flow of the program's instructions.[3] When a Python script encounters a situation that it can't cope with, it raises

an exception. An exception is a Python object that represents an error.[3] When a Python script raises an exception, it must either handle the

exception immediately otherwise it would terminate and come out. [3]

Handling an exception: If you have some suspicious code that may raise an exception, you can

defend your program by placing the suspicious code in a try: block. [3] After the try: block, include an except: statement, followed by a block of

code which handles the problem as elegantly as possible.[3]

Exception

The example adapted from [3]

Exception

try: fh = open("testfile", "w") fh.write("This is my test file for exception handling!!")except IOError: print ("Error: can\'t find file or read data")else: print ("Written content in the file successfully") fh.close()

Exception

It related to class and object.

Detail about Class and object will be explained next time!

Main points of Assignment 2

Input stored in a list

Judge the input format

get the date, month and year from the list

Judge the year, month and date is OK or not

print the right result

Reference

[1] http://homepage.cs.uiowa.edu/~slonnegr/plf/Book/Chapter1.pdf

[2] http://en.wikipedia.org/wiki/Computer_program

[3] http://www.tutorialspoint.com/python/