The original definition of structured programming presented by Edsger Dijkstra was provided to facilitate program proving. The constructs he recommended (IF-THEN-ELSE, DO-WHILE, etc) have now become so commonplace (though program proving has not) that their use is now called "programming" rather than "structured programming." It is important to note; however, that not all "structured" programs are good. One can write incredibly obscure programs that are still structured. Structure is almost a necessary, but far from a sufficient, condition for quality programming.
Reference:
Yourdon, E., How to Manage Structured Programming, New York: Yourdon, Inc., 1976.
