* Control statements

*** Outline

***** Introduction

******* What are we going to do?

******* How are we going to do?

******* Arsenal Required

********* working knowledge of arrays

*** Script

    Welcome. 

    In this tutorial we shall be covering conditional statements and

    control loops. We have used them already in some of our previous

    sessions with brief introduction. We shall be covering 'if-else' 

    statement, 'while' and 'for' loops.

    For understanding of conditional statement we will write a python

    script. Open Scite text editor by going to Applications->

    Programming->Scite:

    First we prompt user for entering a integer by using raw_input

    x = int(raw_input("Enter an integer: "))

    we convert the input string to 'int'

    if x < 0:

    We check if number is less then zero

        if condition is true we print 

        print 'Be positive!'	

	note the indentation

    elif x == 0:

        This is else-if condition and corresponding message

	end of previous indentation indicates ending of a block

        print 'Zero'

    elif x == 1:

        print 'Single'

    else:

        This is else block which is executed when all if, and else

	if statements fails.

        print 'More'

    Save this script in home folder with name '.py'	

    To run this script inside IPython we first start interpreter and 

    type 

    %run '.py'

    It will prompt us to enter a integer and based on our input it 

    prints appropriate message. 

    Python supports only if-elif-else conditional constructs, 

    switch-case statements are not available/supported in Python.

    We can use binary operators like and/or/not to check for multiple

    conditions.

    Now lets look at loop constructs available. Python supports 'while'

    and 'for' statements. We will write a script to understand 'while'

    statement. In Scite click on 'new' file shortcut to open a new tab

    We shall write a script for printing all fabonacci numbers less then

    10. In this series Sum of previous two elements defines the next 

    element.

    First we initialize two variable to first and second number of 

    series

    a, b = 0, 1

    while b < 10:

        This block will be executed till this condition holds True

        print b,

	Note ',' here for printing values in one continues line.

	a, b = b, a+b

	This is one powerful feature of Python, swapping and assigning

	new values at the same time. After this statement a will have 

	present 'b' value and b will have value of 'a+b'(phew this can be close)

    Save this file as 'fabonacci.py' and lets run it from IPython 

    interpreter by

    %run fabonacci.py

    'for' in python works any kind of iterable objects. In our 

    previous sessions we used 'for' to iterate through files and lists.

    So in case we want to get square of say first five numbers using 

    'for' loop, we will have to create a list. For this we will use 

    'range' function available. Lets take a look at documentation 

    available for 'range' function by typing

    range?

    It takes three arguments, first being the start/initial value

    second one being stop/last value and third being the step size. 

    Out of these 'start' and 'step' arguments are optional.

    So if we use range to get first five number it would be 

    range(5)

    Note here that last/stop value is not included in resulting 

    list. So to get square of first five number all we have to do is

    iterate over this list.

    for i in range(5):

    ....print i, i*i

    ....

    ....

    Similarly to get square of all odd numbers from 3 to 9 we can do 

    something like

    for i in range(3, 10, 2):

    so the list returned from range this time will start from 3 and 

    end at 10(excluding it) with step size of 2 so we get odd numbers

    only

    ....print i, i*i

    ....

    ....

    That brings us to the end of this tutorial. We have covered solution

    of linear equations, finding roots of polynomials and non-linear

    equations. We have also learnt how to define functions and call

    them. 

    Thank you!

*** Notes