Here is an implementation for a restricted
find method, where the target is a single character.
In a sense,
find is the opposite of the indexing operator. Instead of taking
an index and extracting the corresponding character, it takes a character and
finds the index where that character appears for the first time. If the character is not found,
the function returns
while loop in this example uses a slightly more complex condition than we have seen
in previous programs. Here there are two parts to the condition. We want to keep going if there
are more characters to look through and we want to keep going if we have not found what we are
looking for. The variable
found is a boolean variable that keeps track of whether we have found
the character we are searching for. It is initialized to False. If we find the character, we
found to True.
The other part of the condition is the same as we used previously to traverse the characters of the
string. Since we have now combined these two parts with a logical
and, it is necessary for them
both to be True to continue iterating. If one part fails, the condition fails and the iteration stops.
When the iteration stops, we must ask a question to find out the individual condition that caused the termination, and then return the proper value. This is a pattern for dealing with while loops with compound conditions.
This pattern of computation is sometimes called a eureka traversal because as
soon as we find what we are looking for, we can cry Eureka! and stop looking. The way
we stop looking is by setting
found to True which causes the condition to fail.