MPL Documentation

Doing Blocks of Code

Program First;

uses Display;


   Write('Are you over 21?');
   If (Ch='Y') or (Ch='y') then Begin
      Write('Adult features enabled.');
   else If (Ch='N') or (Ch=n') then Begin
      Write('Regular features enabled.');
   else Begin
      Write('!! INPUT ERROR !!');

Source Explanation

  1. Program is a file header - letting Modern Pascal know this is a program. In this case, named "First".
  2. uses informs Modern Pascal additional run-time libraries to load. In this case, the keyboard and display library "display".
  3. var is the keyword to inform Modern Pascal that CH is of type CHARACTER.
  4. Begin ... End. is the main code block - the instructions that produce this algorithm of this program.

Code Block Explanation

  1. ClrScr stands for "Clear Screen" and erases everything in the command prompt (console, terminal).
  2. Write displays everything between the apostrophes (known as a string).
  3. ReadKey makes the program wait until the user presses any key, and stores the KEY character in the variable CH.
  4. if ... then is a comparison. If the expression CH equals Y or CH equals y then begin multiple instructions.
  5. else if ... then is another comparison. If the expression CH equals N or CH equals n then debug multiple instructions.
  6. else if the previous comparisons are not true, this is the catch all - begin multiple instructions.

Take Away(s)

  • Notice the semicolon is still on the last IF THEN ELSE instruction in these comparisons.
  • However, the instructions between BEGIN and END also end with a semicolon.