String length in stored procedure, how?

The situation is as follows:

DECLARE v_len INT;

I would have hoped for something like the following to work:

v_len = strlen("Hello");

v_len := strlen("Hello");

v_len = length("Hello");

etc.

but activation fails.

The following gets successfully activated but fails with a "search table error" during run-time:

v_len := ('strlen("Hello")');

The only functionality referring to string lengths that I have encountered are in regard to CE_CALC, but I cannot figure out how it could be used in a case like this or when determining the length of the content of a scalar variable.