How do I add to specific parts of an array?

Say for example I have A = 5 2 7 4 1 6 3 8 B = 4 7 2 5 8 3 6 1

How would I go about adding B to only values in A that are above 4? so the result is C = 9 2 9 4 1 9 3 9 I know I can use A(A>4) this will give me all values above 5 but I don't know how to add B to those specific values. Just to be clear I don't want to add the lines this is just a simple example the one I am working on is 4000x4000 with the values are more random and have no simple order to them.

Answer 1

[KSSV]

A = [5 2 7 4 1 6 3 8 ] ;
B = [4 7 2 5 8 3 6 1];
 iwant = A ;
 iwant(A>4) = A(A>4)+B(A>4)

[Thomas Hoyle]

Thank you