How does one fulfill a vow to fast, and is it necessary for the fasting to be continuous or is it permissible to separate the days?

A conditional vow of obedience is disliked, but it must be fulfilled if the condition it was made upon occurs. So, if you vowed to fast a certain number of days and forgot their count, you must strive to ascertain the number and fast what becomes clear to you. If you remain unsure, many scholars hold that you must fast the greater number to absolve yourself with certainty. Some have held that the minimum number is obligatory, but fasting the greater number is better as a precaution, for either it is the obligatory amount, thereby achieving absolution, or it is a supererogatory act for which you will be rewarded. Consecutive fasting is not required unless you intended it.