The main aim of the thesis is to determine, how the order of functions in the source code will affect the program comprehension while reading a source code, but also the way of reading itself. In this work, we have added a few hypotheses, which will be accepted or rejected based on obtained data from experiments. In experiments, programmers will read two types of source codes. The first one, where the main function is on the top and the second one, where the main function is on the bottom of the source code. Experiments are taking place in UX lab at the faculty. The effect of the functions’ layout is determined by scanning the information about gaze while reading the source code. To make programmers study the whole source code, there was the task given to them to find errors in the source code.