that they be consecutive. For example, in BASIC: 10 LET X = 3 20 PRINT X In other languages such as C and Ada, a label is an identifier, usually appearing at the start of a line and immediately followed by a colon. For example, in C: Success: printf("The operation was successful.\n"); The language ALGOL 60 allowed both whole numbers and identifiers as labels (both linked by colons to the following statement), but few if any other ALGOL variants allowed whole numbers. Early Fortran compilers only allowed whole numbers as labels. Beginning with Fortran-90, alphanumeric labels have also been allowed. Goto The goto statement (a combination of the English words go and to, and pronounced accordingly) is the most basic form of unconditional transfer of control. Although the keyword may either be in upper or lower case depending on the language, it is usually written as: goto label The effect of a goto statement is to cause the next statement to be executed to be the statement appearing at (or immediately after) the indicated label. Goto statements have been considered harmful by many computer scientists, notably Dijkstra. Subroutines The terminology for subroutines varies; they may alternatively be known as routines, procedures, functions (especially if they return results) or methods (especially if they belong to classes or type classes). In the 1950s, computer memories were very small by current standards so subroutines were used mainly to reduce program size. A piece of code was written once and then used many times from various other places in a program. Today, subroutines are more often used to help make a program more structured, e.g., by isolating some algorithm or hiding some data access method. If many programmers are working on one program, subroutines are one kind of modularity that can help divide the work. Sequence In structured programming, the ordered sequencing of successive commands is considered one of the basic control structures, which is used as a building block for programs alongside iteration, recursion and choice. Minimal structured control flow In May 1966, Böhm and Jacopini published an article in Communications of the ACM which showed that any program with gotos could be transformed into a goto-free form involving only choice (IF THEN ELSE) and loops (WHILE condition DO xxx), possibly with duplicated code and/or the addition of Boolean variables (true/false flags). Later authors showed that choice can be replaced by loops (and