in the attachment i have included a code that compiles in Step 7 V5.5. But does not in Tia Portal V13. The FC has a DB_block as input, from that DB i need an integer to use  as a array number for a Global DB. This Global DB has an array of struct and optimized block acces is off. How to do this in Tia Portal?

The concept has changed a bit between STEP7 V5.x and STEP7 V1x (TIA). Even between the various TIA versions, there are differences. The S7-1200 has instructions to deal with indirect addressing instead of the "tradisional" method, while the S7-1500 has it all

Please have a look at..

[LINK1]

[LINK2]

[LINK3]...............most helpful for your problem