Getting 0 when trying to calculate slope

Question

Here is the specific equation that's giving me 0 when it should be giving me -0.4 (-2/5)

slope2 = ((yVals[i+2] - originY) / (xVals[i+2] - originX));

(-2 - 0) / (2 + 3)

slope2 is a double

yVals[] is an int array

origin is an int

Why does it keep returning 0? I know the variables are being called correctly because I've done a println on the different vals and they are correct.

Answer 1

You are performing integer division in Java, where math done using ints must yield an int, so the division truncates anything beyond the decimal point. This means that in Java, -2 / 5 is 0. It's not enough that the target of the assignment is a double. One of the operands must be double (or float) to force floating-point arithmetic.

Cast one of the operands to the / operator to a double to force floating-point arithmetic.

slope2 = ( (double) (yVals[i+2] - originY) / (xVals[i+2] - originX));