Manipulating Text

1. Manipulating Text In today’s lesson we will look at: • why we might want to pick out parts of text strings • some BASIC functions that can be used to chop up text

2. Why Process Text? • There might be occasions when a particular piece of information can be presented in different ways. • Think about a person’s name – you might want to display: • the whole name – e.g. Andrew Virnuls • just the forename – e.g. Andrew • initial and surname – e.g. A Virnuls • However, your user wouldn’t be very happy if you asked them for all the possible versions of their name!

3. Concatenation • The simplest thing you can do with text strings is join them together – this is called concatenation • We looked at this in lesson 2 – we can use the + operator to join words, e.g. forename$ = “Andrew” surname$ = “Virnuls” fullname$ = forename$ + “ “ + surname$

4. String Length • Sometimes you need to calculate the length of a string – e.g. to make sure that it will fit on the screen, or to check that it has the right number of characters (e.g. a bank sort code has 6 digits) • There is a function called len() that tells you how long a string is, e.g. input “Please enter your sort code: ”; sortcode$ chars = len(sortcode$) if chars <> 6 then print “That doesn’t look right!”

5. Characters from the Start • Sometimes you might want to take part of the string from the left hand end. • You can do this using the left$() function – you give it the string and the number of characters you want, e.g. input “What is your name? ”; forename$ initial$ = left$(forename$, 1) print “Your first initial is ”; initial$

6. Characters from the End • There is a corresponding function called right$(), which gives you characters from the end of the string. • For example... input “What is your name? ”; forename$ last$ = right$(forename$, 1) print “Your name ends with ”; last$

7. Characters from the Middle • Should you want to take some characters from the middle of a string, there is a function called mid$() • You tell it the string, where you want to start, and the number of characters, for example... input “What is your name? ”; fore$ middle$ = mid$(fore$, 2, len(fore$)-2) print “The middle of your name is ”; middle$

8. Finding a Character • If you want to know if your string contains a particular character, you can use instr() • You give it a string and a character, and it returns the position of the first occurrence of the character within the string, for example: a$ = "hello world" print instr(a$, " ") • If the character doesn’t appear in the string, the output of instr() is 0.

9. Putting It All Together • What code could you use to separate a full name into a forename and a surname? input "What is your full name? "; fullname$ space = instr(fullname$, " ") forename$ = left$(fullname$, space) surname$ = right$(fullname$, len(fullname$)-space) print "Your forename is "; forename$ print "Your surname is "; surname$ • Using right$() can sometimes be a bit tricky because you are counting characters backwards from the end of the string.