CS 140
Practice problems for Functions

Here are some practice programming problems using functions. These are not to be handed in, though you should feel free to ask questions about any of them outside of class. Remember that programming is an activity that you learn by doing.

1. Write a program with a function next(n) that returns the number after n ( i.e, it returns n+1). Give your program the following main() function:
   
   def main():
         print next(35)
         print next( next(23) )
   
   Your program should print the value 36, then 25.
   
2. In class on 2/22 we developed a program to find perfect numbers (numbers whose factors sum to the number, such as 6 and 28). The key to this was a function isPerfect(x) that returns True if x is a perfect number. See if you can write this program on your own. If you get stuck you can look at the code we developed in class.
   
3. Write a function printTime(minutes) that inputs a number of minutes and prints this in terms of hours and minutes. For example, printTime(325) should print "6 hours and 25 minutes."
   
4. Write a program with area functions for squares, circles and rectangles. You might call these functions AreaSquare(side), AreaCircle(radius) and AreaRectangle(length, width). If you call these functions within the main() function:
   
   def main():
        print AreaSquare(4)
        print AreaCircle( 10 )
        print AreaRectangle( 6, 7)
   
   the program should print 16, then 314.16, then 42
   
5. Write a function decade(year) that takes as argument a year and returns the start of the decade containing this year. For example, for argument 1968 the function should return 1960; for 1999 it should return 1900, and so forth. There are two ways to do this: you can either use the % operator (1968 % 10 is 8, so 1968 - (1968%10) is 1960 ) or you can have a loop that counts down by 10's from some upper limit (say 3000), and stops when it gets a decade smaller than or equal to the year.
   
   Once you have function decade(year) written you can add the following main() function:
   
   def main():
          y = 1
          while y != 0:
                y = input( "Enter a year, 0 to exit: " )
                if y != 0:
                    print "Year %d was part of the %d's" %(y, decade(y) )
   
   On an input like 1968 the program will print
   "Year 1968 was part of the 1960's."
   Of course, for the 1960's it should add "Now that was a groovy decade."
   
6. Write a function deleteB(string) that removes all the instances of the letter "b" from a string and returns the result. Here are two hints. First, you can use a for loop to run through the letters of a stirng:
         for letter in "blah":
              print letter
   will print first "b", then "l", then "a", then "h".
   Second, you can use concatenation to build up strings. Start variable result as the empty string:
        result = ""
   Then use the +-operator to add lettes onto result. For example, you can copy a string with
        result = ""
       for letter in "blah":
            result = result + letter
   
   Finally, give your program a main function to test this out:
   def main():
          print deleteB("bob is a blob")
   will print "o is a lo", a far nicer string.