Fortran 77 (F77) - How to Convert Integer to String and Concatenate

Recently was working with a 91-year old researcher on their Fortran 77 code written over the last 50-years. It needed debugging and some new coding so it lead to learning an ancient language lovingly called F77. It is an eye-opening experience to realize you are working on something with that much history and contributing to a legacy.

Anyhow, personal reflections aside, here is how you convert an integer into a string in fortran 77 and then concatenate it to another string. Useful for suffixing a filename for example.

Conversion

The basic idea behind converting a variable of any type to a string in Fortran 77 is to write that variable into a Character array variable of some length using the Write function. So in our case we will be writing an Integer into a Character array.

Note: The size of the character array should match the number of digits else you will have a lot of white space. Of course you can do that if you want.

Let's define two such variables and assign them values.