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Gri Commands
1: Introduction
2: Simple example
3: Fancy example
4: Running Gri
5: Programming Gri
6: General Issues
7: X-Y Plots
8: Contour Plots
9: Image Plots
10: Examples
11: Handling Data
12: Gri Commands
13: Gri Extras
14: Evolution of Gri
15: Installing Gri
16: Gri Bugs
17: System Tools
18: Acknowledgments
19: License
20: Newsgroup

21: Concept Index
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12.49: The `while' Command

`while .test.|{rpn ...}'
Perform statements in loop while the value of `.test.' or the RPN expression is nonzero. The end of the loop designated by a line containing the words `end while'. The value `.test.' may be an rpn expression. To leave the loop prematurely, use a `break' statement. Upon encountering a `break' statement, Gri jumps to the line immediately following the loop. If the `-chatty' option is nonzero, a notification is printed every 1000 passes through the loop, as a debugging measure to catch unintended infinite loops. Examples:
  • Loop forever, printing a message over and over. 
    while 1
  show "This loops forever. Need to 'break'"
end while
  • Repeatedly read two numbers, and plot a bullet at the indicated location. If (or, hopefully, ``when'') the end of the file is encountered, break out of the loop; otherwise continue plotting forever. 
    while 1
  read .x. .y.
  if ..eof..
    break
  end if
  draw symbol bullet at .x. .y.
end while
  • Loop 10 times, printing the values of `.i.' as they range 0, 1, ..., 9. After exiting from the loop, `.i.' will equal 10. Be careful to use the correct rpn greater-than test to avoid an infinite loop. 
    .i. = 0
while {rpn .i. 10 >}
  show .i.
  .i. += 1
end while
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