If you get a strange result from a formula, check the values of all the variables in the formula. Choose numbers for labeling statements in some logical fashion. If statement numbers are picked at random, the same number may be used more than once, resulting in an error. When an error can be anticipated, catch it and print a message explaining the error along with the values that caused the error. Be careful with all spelling.
Computer code requires precise spelling of all identifiers.
O and the digit 0, the letter l and the digit 1, since the computer treats these characters differently. All loops should be designed to terminate eventually, regardless of possible data errors. This may require the counting of the number of times a loop has executed and stopping after a certain maximum number is reached.