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Beginners  often need "bootstrap" examples to get them started.  I've written dozens of these simple apps to provide this kind of sample code over the years.  This page may provide a place to post those that seem most useful.  

 Recently I've received several requests for help with a few Delphi techniques that are not too difficult once you do one.  Here is the current offerings: 

• Image manipulation (Parking Lot) - how to draw a picture and respond to clicks on a TImage control.
• TChart - graphing a function or other data by passing an array of values.  
• BackTracking Demo illustrates a Depth-first search for a path  through an array meeting certain conditions.
• DrawDice   draws random dice images.
• CountWords counts words in input text.
• Expressions 864 finds all permutations which sum to a given value and use all digits 1-9 exactly once in the equation. 
• Allwords displays all letter permutations or valid words only from a given set of letters.  
• MemLeakDemo illustrates the hazards of allocating and not freeing memory, and how to tell if it is happening..
• Draw Olympic Rings shows how to use "ellipse" and "arc" procedures to draw an image of the Olympic Rings logo.
• Simple Decrypt  implements an ancient shift cipher, "Caesar's Cipher" to encode or decode text messages. 

Features and techniques illustrated are used in a number of programs on DFF, but it's easy to lose the essential characteristics in programs that may have 1,000 or more lines of code.   Each of these programs contains less than 100 lines.

Scroll down to see all offerings.

Image Manipulation (ParKing Lot)

The Image program is a "Parking Lot Simulation" that draws some parking spaces on the canvas of a TImage control.  Clicks on the spaces then show or hide automobile pictures in the spaces.   A TImage has the advantage over a TPaintBox because it can refresh itself when necessary.  Once the canvas has been drawn or modified, the image will be managed by TImage redrawn without our help if the image is moved or minimized or has other forms popup over it.     This is not the case with a TPaintBox where it is the programmer's job to make sure that it knows how to repaint itself at any time.

Click here to download Parking Lot Simulation source code

TChartDemo1 and TChartDemo2

TChart is a powerful graphing and charting facility distributed with most versions of Delphi.   It is so powerful that the hundreds of options can be rather intimidating for the beginner.  Fortunately most features have reasonable defaults and need not be changed.  Most of the rest can be defined a design time in a TChart Edit component that is accessible by a right click or double click on the TChart control image on the form.  Any of the properties can also be defined at run-time.  In this  demo, TChartDemo1,  line plots of two functions are drawn and some of the titles etc. are set via code just to illustrate the technique.

Addendum December 2, 2005: A viewer recently asked about getting user input data from a list box or memo into a chart.  Here's TChartDemo2 which shows a few additional techniques for charting user data.   It includes a "missing" Delphi function, StrToFloatDef. which tries to convert an input string to a floating point number and returns  either the numeric value of the string or a default value if the input string does not represent a valid number. 

  Click here to download TChart Demos source code

BackTracking

Four cells in a 4 x 4 array are randomly loaded with the letters 'A', 'B', 'C', and 'D'.  Four additional cells are loaded with the letter ''X' - these are blocked cells and may not be occupied. The other 8 cells may be passed through while picking up the A, B, C, D cells.  We need to find a path from 'S'  through all of the A, B, C, D cells by moving horizontally and vertically and without visiting any square twice.

Click here to download  Backtracking Demo source code

Addendum June 8, 2005:  Here are three more additions:

DrawDice

A simple program to draw two random dice each time a button is clicked.  
Click Here to download DrawDice source

CountWords

How do you count words in a text document?  Like loving a porcupine - very carefully.  Here's simple start though, with a Getword routine which looks for a predefined set of delimiters marking the ends of  words.  Words from a text file are extracted and listed.  There is also a Summarize button that accumulates number of occurrences  by word.

Click here to  download CountWords source code.

Expressions864

Find all solutions where the sum of two numbers equals 864. And by the way, the 
solution, including the "864" sum must contain all of the digits 1 through 9 exactly 
once.  Other sums to try: 594, 783,  675, 927.  You can also check Brute Force for another mode generalized approach to solving the problem.  Expressions864.prb is now included among the  sample problems. 

Click here to  download Expressions864 source code.

Addendum September 30, 2005  

Allwords

Given a letter string, find all possible subsets of letters ("words") that can be formed.  Optionally, list only words that can validated against  a given dictionary.   This code is fairly simple because it uses two other pre-built units as helper "tools".  UComboV2 contains the class which generates the permutations which help us form the words.  UDict contains the dictionary class that lets us validate our trial words.     

Click here to download   AllWords source

Click here to download AllWords executable

MemLeakDemo

Even though the use of records and pointers is less critical today than in the pre-object days, some schools still teach their use.  And the use of record pointers in the objects field of TStringlists is sometimes convenient.  

The cardinal rule when allocating memory within your program is to make sure that it gets released. One common way to create a memory leak is to allocate a record  using the New function and not releasing the memory (using Dispose).   

Students are sometimes confused by the fact that local variables within functions and procedure are automatically released by Delphi when you exit the routine. This applies to all of the memory that Delphi allocated on your behalf, but not to the memory you allocated. If 
you have local variable, P, and execute New(P) within the routine, Delphi will delete the 4 bytes occupied by P, but not the memory that P points to!   And if not deleted before you exit, that memory will remain allocated until the program ends.   

Here's a program that allocates 1000 byte records within a procedure with and without releasing them just to illustrate the problem.  It uses the AllocMemSize global variable to show increasing memory usage as the program runs.  

Click here to download MemLeakDemo source

Addendum February 15, 2006

Draw Olympic Rings

Every two years. "Olympic Rings" leads the list of search phrases at DFF.  Drawing the rings in Delphi is an interesting drawing exercise, especially if we want them to appear to be interlaced.

Click here to download  Draw Olympic Rings source

Click here to download Draw Olympic Rings  executable

Addendum March 12, 2006

Simple Cipher

We have a decryption program elsewhere at DFF which checks all possible substitution ciphers and check results against a dictionary to determine success. The problem is, this approach can run for hours, and if the text contains words not in the dictionary, may not succeed at all.  My  Mensa "Puzzle-A-Day" calendar periodically contains messages encrypted with a simple "shift cipher", also known as the "Caesar Cipher" because Julius Caesar used it to encrypt message in ancient Roman times.  In the shift cipher, each letter is replaced by a letter at some fixed distance away in the normal "abcd..."  listing of letters.  For example,  if all plain text  "a"s were replaced by "c"s, then "b"s, becomes "d"s, "c"s becomes "e"s  etc. to produce the encrypted text.    

It takes less than 40 lines of user written Delphi code to scan lines of input text using all 25 possible encryption choices (26 if you count the one that maps each letter back to itself).  You provide the dictionary check scanning the outputs to determine which one is correct.  And, of course it will encrypt as well as it will decrypt!

Click here to download  Simple Decrypt source

Click here to download Simple Decrypt  executable

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