数字字符串从数组java中加起来

I have a project to take a string of an unset amount of numbers together. In the project you have to convert the string to an array of numbers. Then start at the end of the array and add them together. So I guess I am asking is the best way to go about this. My teacher said use divisor and modulus to get the carry over, but that is all he really gave us I have the Int array set set up just cannot get the result to add up right.I have a project to take a string of an unset a