Every program unit is either a main program or a subprogram. If a program is to be executable, it must have a main program. The subroutines and functions are called procedures, which are invoked from other procedures or from the main program. The block data subprograms are handled by the loader. A statement consists of one or more key words, symbolic names, literal constants, and operators, with appropriate punctuation.
Every statement is either executable or nonexecutable.
In general, if a statement specifies an action to be taken at runtime, it is executable. Otherwise, it is nonexecutable. In general, nonexecutable statements are completed before execution of the first executable statement. The first 72 columns of each line are scanned. The first five columns must be blank or contain a numeric label.