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simulating_20resume_20and_20resume_20next [2018/03/31 13:19] – external edit 127.0.0.1simulating_20resume_20and_20resume_20next [2024/01/05 00:21] (current) – external edit 127.0.0.1
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 //by Richard Russell, September 2007//\\ \\  BBC BASIC doesn't have the **RESUME** and **RESUME NEXT** statements sometimes found in other dialects of BASIC. Although there are alternative (and probably better) ways of achieving a similar effect when writing a program from scratch, their absence can be inconvenient when translating programs from another dialect. This article describes how a very similar effect can be achieved in //BBC BASIC for Windows// (version 5.60a or later).\\ \\  Firstly let's review what RESUME and RESUME NEXT do. They are intended for use in an error handler (i.e. a routine activated by **ON ERROR**) and cause execution to continue at the statement that resulted in the error (in the case of **RESUME**) or the statement following the one that resulted in the error (in the case of **RESUME NEXT**).\\ \\  Here is a simple **GW-BASIC** or **QBASIC** program which illustrates the use of RESUME (//don't// try to run it in **BBC BASIC**!):\\ \\  //by Richard Russell, September 2007//\\ \\  BBC BASIC doesn't have the **RESUME** and **RESUME NEXT** statements sometimes found in other dialects of BASIC. Although there are alternative (and probably better) ways of achieving a similar effect when writing a program from scratch, their absence can be inconvenient when translating programs from another dialect. This article describes how a very similar effect can be achieved in //BBC BASIC for Windows// (version 5.60a or later).\\ \\  Firstly let's review what RESUME and RESUME NEXT do. They are intended for use in an error handler (i.e. a routine activated by **ON ERROR**) and cause execution to continue at the statement that resulted in the error (in the case of **RESUME**) or the statement following the one that resulted in the error (in the case of **RESUME NEXT**).\\ \\  Here is a simple **GW-BASIC** or **QBASIC** program which illustrates the use of RESUME (//don't// try to run it in **BBC BASIC**!):\\ \\ 
 +<code qbasic>
         PRINT "Program starting"         PRINT "Program starting"
         ON ERROR GOTO 1000         ON ERROR GOTO 1000
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         Divisor = 3         Divisor = 3
         RESUME         RESUME
 +</code>
 When run the program generates the following output:\\ \\  When run the program generates the following output:\\ \\ 
   Program starting   Program starting
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   Program finished   Program finished
 Note that an error occurs (division by zero) because **Divisor** is initially zero, but in the error handler **Divisor** is changed to 3 and the division is repeated, this time successfully.\\ \\  Here is the same program in //BBC BASIC for Windows// using some sneaky code to reproduce the effect of **RESUME**:\\ \\  Note that an error occurs (division by zero) because **Divisor** is initially zero, but in the error handler **Divisor** is changed to 3 and the division is repeated, this time successfully.\\ \\  Here is the same program in //BBC BASIC for Windows// using some sneaky code to reproduce the effect of **RESUME**:\\ \\ 
 +<code bb4w>
         PRINT "Program starting"         PRINT "Program starting"
         ON ERROR GOTO 1000         ON ERROR GOTO 1000
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         WHILE ?P% AND P% + ?P% < !408 P% += ?P% : ENDWHILE         WHILE ?P% AND P% + ?P% < !408 P% += ?P% : ENDWHILE
         GOTO (P%)         GOTO (P%)
 +</code>
 This code produces the following output:\\ \\  This code produces the following output:\\ \\ 
   Program starting   Program starting
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   Program finished   Program finished
 Here the division isn't repeated, and the RESUME NEXT transfers control to the "PRINT "Program finished"" line.\\ \\  Here is the equivalent program in //BBC BASIC for Windows//:\\ \\  Here the division isn't repeated, and the RESUME NEXT transfers control to the "PRINT "Program finished"" line.\\ \\  Here is the equivalent program in //BBC BASIC for Windows//:\\ \\ 
 +<code bb4w>
         PRINT "Program starting"         PRINT "Program starting"
         ON ERROR GOTO 1000         ON ERROR GOTO 1000
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         REPEAT P% += ?P% : UNTIL ?P% = 0 OR P% > !408         REPEAT P% += ?P% : UNTIL ?P% = 0 OR P% > !408
         GOTO (P%)         GOTO (P%)
 +</code>
 And here is the output:\\ \\  And here is the output:\\ \\ 
   Program starting   Program starting
simulating_20resume_20and_20resume_20next.1522502383.txt.gz · Last modified: 2024/01/05 00:16 (external edit)