Here's a readability tip for working with ASCII numbers: Treat adding and subtracting the ASCIIness as you would multiplying and dividing by a unit in physics.

Here's a readability tip for working with ASCII numbers: Treat adding and subtracting the ASCIIness as you would multiplying and dividing by a unit in physics. You can add '0' to convert a numeral to ASCII and subtract '0' to convert it back, and you can do direct comparisons between ASCII numerals. if(characters[i] <= '9' && characters[i] >= '0') { ret = ret * 10 + characters[i] - '0'; }