According to the invention, simulation code and production code are generated as source code from a model. The model comprises one or more blocks which specify a desired behavior of a program, in particular a control program. At least one of the blocks is marked with a simulation code attribute. Simulation code is generated for those blocks that include a simulation code attribute. Production code is generated for all other blocks. The generated source code includes both simulation code and production code. The simulation code portions are contained in the source code in a separable manner from the production code portions.