This paper deals with the dependability evaluation of software programs of iterative nature. In this work we define a model that is able to account for both dependencies between input values of successive iterations and the effects of sequences of consecutive software failures on the reliability of the controlled system. Differently from previously proposed models, some effort is devoted to address the problem of how to get accurate estimates for the basic parameters. A model is thus proposed that, requiring the designers or users to provide information usually obtainable by experimental techniques, e.g. testing, is more useful and more generally applicable. Then a thorough analysis is performed to highlight the effects of the different parameters on the dependability attributes. This analysis allows to appreciate which effects (and their extent) have variations of both correlation between successive inputs and different structural characteristics of the software at hand. Moreover the robustness of the model against imprecise assessments of the starting parameters is also shown.