Structure Rule One: Code Block

If the entry conditions are correct, but the exit conditions are wrong, the bug must be in the block. This is not true if execution is allowed to jump into a block or jump out of a block. Then the bug might be anywhere in the program. Debugging under these conditions is much harder.

Rule 1 of Structured Programming: A code block is structured. In flow charting terms, a box with a single entry point and single exit point is structured.

This may look obvious, but that is the idea. Structured programming is a way of making it obvious that a program is correct.

In assembly language there is no syntax for showing program blocks. You think about them when you design the program, and when you draw a flowchart. But in coding you just follow your design.