0 is a perfectly good age, plenty of humans have been 0 years old. The point is simply that the first return value of atoi() if the second is non-nil is meaning

0 is a perfectly good age, plenty of humans have been 0 years old. The point is simply that the first return value of atoi() if the second is non-nil is meaningless. Atoi would have been exactly as useful if it had been defined that atoi() returns 167 and an error if it can't interpret the string as an integer. Code which proceeds to use the first return value of atoi() if the second one is non-nil is wrong code, even if it happens to work for some convoluted scenarios. Edit to note: atoi() actually doesn't always return 0 if it fails: if the second return is err.Err=ErrRange, then the first is the max value that can fit on 32 bits.