HP 33s Conditional Instructions, 13–6, 13–6 Programming Techniques

„To  !: {V.

„To a line number: {Vlabel nnnn (nnnn < 10000). For example, {VA0005.

„To a label: {Vlabel —but only if program entry is not active (no program lines displayed; PRGM off). For example, {VA.

Conditional Instructions

Another way to alter the sequence of program execution is by a conditional test, a true/false test that compares two numbers and skips the next program instruction if the proposition is false.

For instance, if a conditional instruction on line A0005 is º/@ (that is, is x equal to zero?), then the program compares the contents of the X–register with zero. If the X–register does contain zero, then the program goes on to the next line. If the X–register does not contain zero, then the program skips the next line, thereby branching to line A0007. This rule is commonly known as "Do if true."

  

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Do next if true.		º/@	€ N	Skip next if false.
	M  	! 	 N
		
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The above example points out a common technique used with conditional tests: the line immediately after the test (which is only executed in the "true" case) is a branch to another label. So the net effect of the test is to branch to a different routine under certain circumstances.

There are three categories of conditional instructions:

„Comparison tests. These compare the X–and Y–registers, or the X–register and zero.

13–6Programming Techniques