# Correlation between two quantitative variables

I have two quantitative variables, one with negative and positive values (let's call it A), and the other with solely positive values (let's call it B). I would want to do the correlation between these two variables. These values are those of individuals (one value per individual). I would like to know if this makes sense to correlate directly with the two variables, or to look the correlation between A and B in two groups : one where individuals have negative values for A and the other group where individuals have positive values for A.

Correlation is invariant under translations of the two variables: $$corr(A,B) = corr(A+k_1,B+k_2).$$ So, it is not meaningful to calculate two separate correlations (unless units with positive and negative values of $A$ have a particular meaning, and you want to consider two separate subpopulations).