SECTION E - PRIMER                                     FILE PRIMER.E
                                  INPUT FROM THE KEYBOARD
                                  ***********************

               Most programs require some information or action from the 
          viewer, even if it is only to respond to a 'Press any key to 
          continue' request. PRIMER looks at the INPUT,LINE INPUT and INKEY$ 
          commands
              An easy way to use the INPUT command is to put it in the form:

                  10 INPUT " What is your first name ?"; name$ 

          The characters between the quote marks will print on the screen to 
          invite a response from the operator, who will type in an answer then 
          press RETURN . The name will be stored as the variable name$, which 
          can then be used as you wish in the program.   Name$, as you can 
          see, is a string variable but if the answer to an INPUT statement is 
          expected to be a number then the variable should be of the numeric 
          type. eg. z or t% ( as explained in section c ) 

          Another way to use the same command is:

              10 PRINT " What is your first name ?  "
              20 INPUT name$

          This method may appear to be long-winded but it's appearance when 
          run may be to your liking for some programs. Check it on the next 
          listing. It comes into it's own when making a multiple choice menu.
              INPUT can be used to store more than one variable, but this is 
          not recommended as it requires more application from the operator.
          The command would take the form ;

              50 INPUT "Name your choices of fruit  1st/2nd/3rd "; a$,b$,c$

          Note that the three names can be stored in variables a$,b$ and c$ 
          and used separately, but unfortunately it involves the operator 
          typing the three choices with a comma between, otherwise the input 
          will not be accepted and you are faced with the  message 'Redo from 
          start', which is a standard BASIC error message.It is usually 
          preferable to use one INPUT line for each variable.

              70 PRINT "Name your choice of fruit in order of preference"
              80 INPUT "First choice" ,first$
              90 INPUT "Second choice " , second$
          etc.
          Punctuation plays it's part as usual in the syntax. There must be a 
          comma or a semicolon between  the prompt in quotes and the variable.  
          A semicolon causes a question mark to be printed , the comma does 
          not. Check this on the next listing.

          A similar command, used in similar ways, is LINE INPUT. This allows 
          the input of lines of script, including commas,which are rejected by 
          INPUT.

          Another useful routine involves the function INKEY$

              40 PRINT" Press any key to continue "
              45 WHILE INKEY$="": WEND

          The familiar 'Press any key to continue' routine is done with the 
          help of the INKEY$ function. INKEY$ monitors the keyboard for a 
          character to be pressed,and reports on it. This information can be 
          used by the computer in various ways. In line 45 above there is a 
          WHILE...WEND loop .We haven't covered this yet, but it is sufficient 
          to know that line 45 will hold up the program until the statement 
          INKEY$ = "" is not true.   "" is a pair of double quotes with 
          nothing in between and is known as a null string. (null = nil, nowt, 
          nothing or zilch, depending on your college) When a key is pressed 
          INKEY$ ="" is no longer true as now INKEY$ = 'the key value pressed'  
          and so the program can proceed. You don't need to bother with the 
          theory unless you wish - just use the routine.

          INKEY$ can also be made to hold up a program until a particular key 
          is pressed. Use the routine :

              80 PRINT "Press C to continue.'
              90 WHILE INKEY$<>C OR INKEY$<>c: WEND
           
          In line 90 a loop is formed by WHILE...WEND  The sign <> means 'is 
          not equal to ' , so when  either upper case or lower case c is 
          pressed line 90 stops looping and the program continues.

          This routine can be modified yet again to use keys or characters 
          which do not appear on the keyboard:

              120 PRINT "Press RETURN to continue"
              130 WHILE INKEY$<>CHR$(13): WEND

          This example is the same as the previous one except for the CHR$(13) 
          This brings into play the ASCII code system which is recognised by 
          your computer. Each character and function has a number allocated to 
          it, and a full table can be seen in the PCW manual, page 113.    
          CHR$ converts the number to it's ASCII character ,and as 13 
          represents RETURN ,bingo. Other useful numbers for this purpose are:
                  27 = EXIT  ,   32 = SPACE BAR 

          End of file PRIMER.E
             
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