Try converting the input to a numeric vector, it will make your life much easier:
>> vec = input('enter provided code: ','s')-'0'
enter provided code: 123456
vec =
1 2 3 4 5 6
and to check if a value is even/odd, try using mod like with a value of 2, not 3:
if mod(vec(4),2)
rvp = vec(6)-vec(5)
else
rvp = vec(5)-vec(6)
end
produces this result (which is correct as vec(4) is even, so the difference vec(5)-vec(6) is calculated:
rvp = -1
