Fix compiler warnings in differentiation and integration tutorials.

...entals-differentiation/completed/LocDifferentiation2D.cpp

...entals-differentiation/completed/StdDifferentiation1D.cpp

...entals-differentiation/completed/StdDifferentiation2D.cpp

...mentals-differentiation/tutorial/LocDifferentiation2D.cpp

...mentals-differentiation/tutorial/StdDifferentiation1D.cpp

...mentals-differentiation/tutorial/StdDifferentiation2D.cpp

...n/fundamentals-integration/completed/LocIntegration2D.cpp

...n/fundamentals-integration/completed/StdIntegration1D.cpp

...n/fundamentals-integration/completed/StdIntegration2D.cpp

...on/fundamentals-integration/tutorial/LocIntegration2D.cpp

...on/fundamentals-integration/tutorial/StdIntegration1D.cpp

...on/fundamentals-integration/tutorial/StdIntegration2D.cpp