SECTION B                                              FILE INTRO.B
                           LINE NUMBERS AND COMMAND LINES
                           ******************************

          The program you have just been working with is a simple example of a 
          BASIC program. I hope that you have spent a little time with it and 
          used the LIST command to reveal how  BASIC looks when written. There 
          is no need at all for the present to attempt to understand how it 
          works, but having seen it we can start to find out how a BASIC 
          program is put together. 
              If you are new to computer programming you may find some of the 
          following difficult to understand straight away. Just read it 
          through carefully, and as you carry on with the course you will find 
          that everything will fall into place.
           
          LINE NUMBERS    MALLARD BASIC is written in lines, each of which         
          ============    commence with a number (not all BASICs do). The 
          lowest possible line number is 0, the largest 65534. A very common 
          way to number program lines is to start at ten and then number in 
          increments of 10 ie 10,20,30,40 etc. Doing this allows extra lines 
          to be inserted if required. Lines may be entered in any order and at 
          the first opportunity BASIC will put them in numerical order. If, 
          for example, an extra line was required between lines 20 and 30, you 
          would give it an intermediate number, say 23, and BASIC would pop it 
          into it's correct numerical niche.
              When writing a long program it is often convenient to make it up 
          of a number of short programs or 'modules'. Each module can be well 
          separated numerically , say starting each module 1000 apart, and in 
          addition these modules can be written in any order, provided the 
          line numbers reflect their true place in the program. BASIC will 
          sort this out and place each line in it's correct numerical 
          position. When the program is complete BASIC allows you, if you 
          wish, to renumber the program for neatness, using the command RENUM. 
          Where one line refers to another, RENUM will take care of this too, 
          provided certain rules are kept. This is how programs in magazines 
          are always numbered so neatly. Only the author will know how many 
          lines he had to insert to make the program work.
              A program line cannot consist of a number on it's own, as BASIC 
          will not recognise it. You will see later that this is a way of 
          cancelling a line of programming.        

         COMMAND LINES   After the line number comes the instruction to the 
          =============   computer, telling it what to do. Writing these 
          instructions so as to make the computer do as you wish is, of 
          course, what programming is all about. When you have written a 
          program line, and are happy with it, you press [RETURN] to fix the 
          line in memory and to prepare the computer to receive the next line. 
          Lines can contain a maximum of 255 characters including numbers, 
          letters, spaces, symbols and punctuation marks; if you attempt to 
          exceed this the computer will not accept it and will beep furiously. 
          Many instructions can be grouped on one line if required. Long lines 
          generally use less memory, but this is seldom very important and too 
          many long lines make a program tedious to write and understand. As 
          with many aspects of programming, line length is a question of 
          individual preference and style

          End of file INTRO.B
cts of programming, line length is a question of