Abstract: A programming tool for providing a graphical representation of the relationships among a plurality of nested blocks integrated into a processed "C" source code listing is disclosed. For each line of code including a "{" character, an outbound arrow is appended. Similarly, for each line of code including a "}" character, an inbound arrow is appended, and the inbound and outbound arrows are tabbed into vertical alignment. A "depth number" is developed for each line now having arrows by performing an increment when a line having an outbound arrow is encountered and a decrement for the starting depth number value of the next line when a given line having an inbound arrow is encountered. The depth numbers, and also one or more (as indicated by the depth number for a given line) right justified vertical line segments, are appended to the lines having outbound or inbound arrows.