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Algorithms and Programming eXercises #15

Compound Data Structures
The ARRAY - Solutions

The following represent strategies/algorithms and NOT actual coded solutions - it is thought there is definite advantage here for students to actually wrestle with the actual code to get a working solution. There may be MANY different ways to encode these solutions - get creative and try to be efficient

1

  1. Your function needs a local byte variable used as a tally of the spaces. The procedure should step through each element of the array (using a for..to..do loop) if an element is a space, inc the tally. At the end of the scan, assign the tally value to the the function name to return it.
  2. the is a simple loop assignment
  3. this needs a loop, and could be achieved through a large case statement (or HA/VHA students might like to use a more efficient index-based tally system)
  4. very similar to part a but instead of looking for a space, you should prompt for and accept a letter into a character variable and then use this variable in the same way you searched for a space
  5. building on the previous part, this is an application of part d's solution
  6. look back to the 'how random is random' exercise to see how you achieved the graph of frequency

2. Unless you can see the pattern, you will have difficulty with this activity. line 1 and 2 are always 1's, but in line 3, you will notice the 2 (which is a sum of the previous line's ones. From thereon, each number is a sum of the 2 digits above it on the previous line. An array can help here to keep the previous line and help you generate the next line


Strings

1, 2, 3: these are 'try and see' what happens exercises that test your understanding of string functions.

4. This is a 'head' or 'tail' exercise - the 'head' is the stuff at the beginning od the string, the 'tail' is the last few characters. You would use length(FRED) to determine how many chars are in fred, and then some maths using 'n' to determine the character positions you are interested for each of the parts to this exercise

5.

  1. this should be a relatively simple task of stepping along the string, replacing each character with it's upcase value. Remember upcase does nothing to characters that are not lower case letters
  2. trim can be achieved by scanning a string, deleting spaces until you reach a non-space - this will eliminate the head spaces. To eliminate the tail spaces, you could continually delete the last character if it is a space
  3. to deblank, you could use a pre-tested indefinite loop that finds the position of a space in the string, and deleting it. The loop should terminate when the pos returns a zero
  4. collapse could be achieved by looking for double spaces and replacing them with single spaces - use a pre-tested indefinite loop to contiue doing this while double spaces are found
  5. overwrite requires you to use delete and then insert
  6. replace also requires you to use pos and then delete and then insert. take care that you test to see if the substring is actually there before replacing it, otherwise 'odd' results will occur int he beginning of the string
  7. replaceall is a little more tricky - like parts c and d, you need to loop whilst you find the substring, replacing it as you go - stop when there are no more occurrences of it.

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