operations scope of the variable 'residu' can be reduced

Fix cppcheck issue "[analitza/operations.cpp:264] (style) The scope of the variable 'residu' can be reduced. Warning: Be careful when fixing this message, especially when there are inner loops. Here is an example where cppcheck will write that the scope for 'i' can be reduced: void f(int x) { int i = 0; if (x) { // it's safe to move 'int i = 0;' here for (int n = 0; n < 10; ++n) { // it is possible but not safe to move 'int i = 0;' here do_something(&i); } } } When you see this message it is always safe to reduce the variable scope 1 level. [variableScope]".