Re: @Ian Bush
IIRC variables named i, j, k were automatically of integer type.
All variables were implicitly declared. Any name starting with I, J, K, L, M, or N was integer, anything else was float, unless declared otherwise.
It was common practice, on compilers that supported it, to declare everything to be some unlikely datatype (such as 64-bit boolean) so that mistyped variable names would be picked up by the compiler.
IMPLICIT LOGICAL*64 (A-Z)
(please imagine that line indented by 6 spaces, " " doesn't seem to work here)
Of course ... that's going back a way. Modern Fortran, which isn't quite the oxymoron you might think, doesn't need such tricks.