Introduction to Python loops while and for .pptx

Introduction to Python loops while and for .pptx

• 1.
  Process Control-Loops
• 2.
  VKS-12 LOOPS Iteration
• 3.
  VKS-12
• 4.
  VKS-12  Repeated executionof a set of statements is called iteration  Iteration is achieved in programing language using loop.  The iteration can be definite or indefinite depending upon the user logic  All programming language provides some construct which are used to automatically repeat a set of statements generally called Loops  Python provide two type of loops while and for  while is condition-controlled loop  for is count-control loop For loops are traditionally used when you have a piece of code which you want to repeat n number of times. While Loop is used when a condition is to be met, or if you want a piece of code to repeat forever,
• 5.
  VKS-12 Generally any loopin Python has three (3) components: a) Control Variable and its Initialisation: Generally a loop in Python has a control variable. Control variable is generally an integer type or character type or floating point type. But we can have loop in Python with out a control variable. We will discuss such loops later. If a loop has a control variable then the control variable has to be initialized. b) Terminating Condition: Generally a loop should terminate after certain number of iterations. Terminating condition of the loop in Python is a condition (logical expression) involving the Control Variable. Condition or logical expression plays a very important in the working of a loop in Python since number of times loop is repeated depends on the condition. c) Updation of Control Variable: Every Python loop repeats statement or block. Inside the block or statement of a loop, control variable is updated (value of the control variable is either incremented or decremented), so that the loop terminates after certain number of iterations.
• 6.
  VKS-12 Loop through aset of statements as long as a condition is true Syntax while(Condition) : Python Statement(s) Updating of control variable The (condition) may be any Python valid logical expression. When program execution reaches a while statement, the following events occur: 1. The (condition) is evaluated. 2. Condition is TRUE (nonzero), the Block / Statement is executed. 3. Inside the Block / Statement, control variable is updated and Condition is tested once These three steps are repeated till Condition is FALSE. When the condition is evaluated to be false, the loop is terminates.
• 7.
  VKS-12 k<=5 print(k) k+=1 TRUE1 2 TRUE 2 3 TRUE 3 4 TRUE 4 5 FALSE Loop terminated TRUE 5 6
• 8.
  VKS-12 K<=20 print(k) K+=2 True2 4 True 4 6
• 9.
  VKS-12 range() Function range() generatesa list of numbers, which is generally used to iterate over with for loop. Often you will want to use this when you want to perform an action for fixed number of times. Function range() has three syntaxes.
• 10.
  VKS-12 1. range(StopVal) generatessequence of integers 0, 1, 2, 3, …, StopVal-1 Start value of the sequence is always 0 (zero) when range() function has single parameter. range(6) will generate sequence of integers 0, 1, 2, 3, 4, 5 range(11) will generate integers 0, 1, 2, 3, …, 9, 10 range(0) or range(-5) does not generate an any sequence because 0>StopVal
• 11.
  VKS-12 2. range(StartVal, StopVal)generates integers StartVal, StartVal +1, StartVal +2, , …, StopVal-1 range(1, 6) will generate sequence of integers 1, 2, 3, 4, 5 range(6, 11) will generate sequence of integers 6, 7, 8, 9, 10 range(-3, 4) will generate sequence of integers -3, -2, -1, 0, 1, 2, 3 range(3, 0) or range(3, -4) does not generate an any sequence of integer because StartVal>StopVal
• 12.
  VKS-12 3. range(StartVal, StopVal,Step) a) Generates integers StartVal, StartVal + Step, StartVal + 2*Step, …, StopVal-1 When StartVal<StopVal and Step>0 Generates a sequence in ascending order. b) Generates integers StartVal, StartVal - Step, StartVal - 2*Step, …, StopVal+1 When StartVal>StopVal and Step<0
• 13.
  VKS-12 Generates a sequencein descending order. range(1, 6, 1) will generate sequence of integers 1, 2, 3, 4, 5 range(2, 12, 2) will generate sequence of integers 2, 4, 6, 8, 10 range(1, 12, 2) will also generate sequence of integers 1, 3, 5, 7, 9, 11 range(-1, -6, -1) will generate sequence of integers -1, -2, -3, -4, -5 range(15, 2, 3) will generate sequence of integers 15, 12, 9, 6, 3 range(-15, -2, 3) will generate sequence of integers -15, -12, -9, -6, -3 range(-5, 6, 2) will generate sequence of integers -5, -3, -1, 1, 3, 5 range(-9, 0, -2) does not generate an any sequence because StartVal<StopVal and Step is -2