Size

LOC is the most common way of quantifying software size; however, this cannot be done until the coding process is complete. Function points have the advantage of being measurable during the design phase of the development process or possibly earlier.

Lines of Code

This is probably the most widely used measure for program size, although there are many different definitions. The differences involve treatment of blank lines, comment lines, nonexecutable statements, multiple statements per line, multiple lines per statement, and the question of how to count reused lines of code. The most common definition counts any line that is not a blank or a comment, regardless of the number of statements per line. In theory, LOC is a useful predictor of program complexity, total development effort, and programmer performance (debugging, productivity). Numerous studies have attempted to validate these relationships.

Function Points

J. Albrecht proposed a metric for software size and the effort required for development that can be determined early in the development process. This approach computes the total function points (FP) value for the project, by totaling the number of external user inputs, inquiries, outputs, and master files, and then applying the following weights: inputs (4), outputs (5), inquiries (4), and master files (10). Each FP contributor can be adjusted within a range of ±35% for a specific project complexity.

Complexity

More metrics have been proposed for measuring program complexity than for any other program characteristic. Two examples of complexity metrics are:

Cyclomatic Complexity -- v(G)

Given any computer program, draw its control flow graph, G, where each node corresponds to a block of sequential code and each edge corresponds to a branch or decision point in the program. The cyclomatic complexity of such a graph can be computed by a simple formula from graph theory, as v(G)=e-n+2, where e is the number of edges, and n is the number of nodes in the graph.

Knots

Calculate program knots by drawing the program control flow graph with a node for every statement or block of sequential statements. A knot is defined as a necessary crossing of directional lines in the graph. The same phenomenon can be observed by drawing transfer-of control lines from statement to statement in a program listing