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CISC 101: Fall 2011

CISC 101: Fall 2011. Hossain Shahriar shahriar@cs.queensu.ca. Announcement and reminder!. Tentative date for final exam need to be fixed! Topics to be covered in this lecture(s) More on range function While loop Break. Range function. >>> range(5)

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CISC 101: Fall 2011

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  1. CISC 101: Fall 2011 HossainShahriar shahriar@cs.queensu.ca

  2. Announcement and reminder! • Tentative date for final exam need to be fixed! • Topics to be covered in this lecture(s) • More on range function • While loop • Break

  3. Range function • >>> range(5) • [0, 1, 2, 3, 4] # we are getting one less element that expected • >>> range(5, 10) • [5, 6, 7, 8, 9] # we are getting one less element that expected • >>> range(4, 12, 3) • [4, 7, 10] • >>> range(-10, -100, -30) • [-10, -40, -70] • Write a program that sum the series: 2+ 4+ ..+ 10 • sum =0; • For i in range (2, 12, 2): • sum+= i

  4. While loop • while expr1 : • statement • Two things to keep in mind for using while loop • expr1 must include an iterating variable • You are responsible for incrementing/decrementing the iterating variable to terminate the loop • Let us sum the series: 2 + 4+ … 10 [watch the red lines!!] • sum =0 • i=2 • while i < 10: • sum+= i • i+= 2

  5. Loop (cont.) – Break statement • Useful in certain situations and often used in an if-else structure within a loop • Imagine, we want to iterate a list to find at least one negative number • We do not need to continue the loop once we find a case • for x in len (list) • If x < 0: • Print ‘found a negative number, goodbye!’ • break • Caution: if you have multiple loops, then break will only affect the immediate loop where it is located • For …. : #loop1 • For … : #loop2 • If … break # break loop2 only and loop1 will continue as usual

  6. Loop (cont.) – Break statement • Take home assignment: (3 marks) • Write a program that checks if a given number N is prime or not. • Tips: N is a prime number when it not divisible by any number other than 1 and N • You need to use a for/while loop, if-else, and a break statement • Iterate from 1 to N/2 and check the remainder is always non zero to conclude that N is a prime number

  7. Exception • A generic way to handle incompatible input • E.g., a user provides string instead of a number • def main(): • try: • x = int (input ("enter a number : ")) • … • except Exception: • print "The supplied input is not a number" • main()

  8. Tomorrow’s class • File handling

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