BBC BASIC has two loop structures: the FOR…NEXT loop and the REPEAT…UNTIL loop. These structures are essential components of most realistic programs in BASIC, and the same is true of assembly language. However, in assembly language the structures do not come ready made as in BASIC, so we need to develop methods of building them up from the component instructions available. In doing this, we will also create a third important structure, regrettably missing in BBC BASIC: this structure we will term the REPEAT WHILE loop. The difference between REPEAT…UNTIL and REPEAT WHILE is that the former will always be executed at least once, since the exit is at the end; the latter need not be executed at all, since the exit is at the beginning.
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- Loop Structure in Assembly Language
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