Unit 4 · Steady
Text that you can look inside but never change. Counting from zero takes some getting used to, and almost every early text bug is a position being one off.
What a strong answer looks like
A strong Unit 4 answer numbers the characters first and says whether the original text was changed, which it never is.
Know
Characters are numbered from zero, so the last one sits at one less than the length. The length itself is never a valid position.
Apply
Write the numbers under the characters before answering anything about position.
Watch out
Asking for the character at the length, which is one past the end.
Study move
Number every character of a short word and name the first and last valid positions.
Know
Taking a portion includes the starting position and stops just before the ending one. Searching returns the position of the first match, or a negative number when there is none.
Apply
Mark both ends on paper before working out the result.
Watch out
Expecting the ending position to be included, which gives a portion one character short.
Study move
Pull out the part of a word before a chosen letter, then try it when the letter is absent.
Know
Every text operation hands back a new piece of text and leaves the original alone. If you do not store the result, nothing happens.
Apply
Store the result of every text operation.
Watch out
Calling an operation and expecting the variable to have changed, which silently does nothing at all.
Study move
Write two lines differing only in whether the result is stored, and predict both outputs.
Know
Looking at every character means looping over the positions. Comparing neighbouring characters means stopping one position early.
Apply
Match the loop bound to what you are comparing.
Watch out
Comparing each character with the next one all the way to the end, which reaches past it.
Study move
Count how many neighbouring characters are the same, and check it on a one-letter word.
Connections and techniques that receive extra attention in this unit.
Related topics some schools attach to this unit and others leave out. Covered on request rather than assumed.
Modeling drill
Write a method that returns the part of an address before the first space, and say what it does when there is no space.
