If statement followed by 5,4,4

[Bob90]

Hi,

I'm new to Fortran. I have a F77 program that has a line

if(VARIABLE-1)5,4,4

What does this do? (I have labels 4 and 5 below if that helps)

I think it checks if Variable > 1, as 0 = false, then goes to labels 5, 4, 4, but that makes no sense.

Obviously searching Google brings nothing as if statements are too common.

Thanks in advance

 

[Bob90]

OK, simples really.

If <0 goto first label
if 0 goto second label
if >0 toto third label.

Sorry!

 

[xwb]

It is the original if statement from Fortran I, based on the assembler at that time. The old machines like IBM, Prime and Data General had a compare instruction followed by a 3 way jump. It is legal up to F77 but not in F90 and above.

Fortran does not have reserved words so it allows a variable to be called if. So you could have an array called if and see a statement like

if (if(m) .gt. 5) if (if(m-1)) 10, 20, 30