get get a number from keyboard into accumulator print print contents of accumulator load Val load accumulator with Val (Val unchanged) store M store contents of accumulator into memory location called M (accumulator unchanged) add Val add Val to contents of accumulator (Val unchanged) sub Val subtract Val from contents of accumulator (Val unchanged) goto L go to instruction labeled L ifpos L go to instruction labeled L if accumulator is >= zero ifzero L go to instruction labeled L if accumulator is zero stop stop running M Num before program runs, set this memory location (called M) to numeric value NumIf Val is a name like Sum, it refers to a labeled memory location. If Val is a number like 17, that value is used directly. So add Sum means to add the contents of the memory location named Sum to the accumulator value (leaving Sum's contents unchanged), while add 1 means to add 1 to the accumulator value.
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This version has a limit of 1000 instructions by default, to make it easier to prevent infinite loops. The single-step version has no limit.