A computer language is the means by which instructions and data are transmitted to computers. Put another way, computer languages are the interface between a computer and a human being. There are various computer languages, each with differing complexities. For example, the information that is understandable to a computer is expressed as zeros and ones (i.e., binary language). However, binary language is incomprehensible to humans. Computer scientists find it far more efficient to communicate with computers in a higher level language.
Block-structured language grew out of research leading to the development of structured programming. Structured programming is based on the idea that any computer program can be written using only three arrangements of the information. The arrangements are called sequential, selection, and iteration. In a sequential arrangement, each programming instruction (statement) is executed one after the other. This order is vital. The execution of the second statement is dependent on the prior execution of the first statement. There is more flexibility built into the selection arrangement, where choices are typically made with an IF...THEN...ELSE structure. Iteration is also known as loop structure. Loop structures specify how many times a loop will be executed. In other words, a command can be executed a number of times until the task is completed.
PASCAL, ALGOL, and MODULA-2 are examples of block-structured languages. Examples of non-block structured languages are BASIC, FORTRAN, and LISP. Refinements of BASIC and FORTRAN produced more structured languages.
Block-structured languages rely on modular construction. A module is a related set of commands. Each module in a block-structured language typically begins with a "BEGIN" statement and ends with an "END" statement.