Which looping structure does not work in FORTRAN?

Answer 1

Unlike many programming languages that generally support for-loops, while-loops and until-loops or some variant of the three, FORTRAN has only one loop structure: the do-loop, which corresponds to a for-loop.

The general form of the FORTRAN do-loop is as follows:

do label var = expr1, expr2, expr3statements

label continue

Where, var is the control variable (or loop index), expr1 is the initial value of var, expr2 is the terminating bound of var, and expr3 is the increment of var. The label must be an unique integer value (usually labels begin at 10 and increment by 10 for all subsequent labels), and denotes the end of the statement or statements that constitute the loop body.

Modern variants of FORTRAN also allow the use of an end do statement which permits the label clause to be omitted completely.

Although FORTRAN has no concept of either a while-loop or an until-loop, these loops can be simulated using label, if and goto statements:

while-loop:

label if (logical expr) then statementsgoto labelendif

until-loop:

label continue statementsif (logical expr)goto label