Update README.md

README.md

@@ -206,6 +206,55 @@ The quotation code is compiled into the enclosing word and bypassed by a jump. A
 
 ## Strings
 
+Strings are surrounded by single quotes and they're immutable. For example `'Hello world'`.
+
+```forth
+'hello world' 0 5 substr \ gets the characters from 0 to 5 (exclusive)
+```
+
+```forth
+'hello world' 1 at \ gets the first character (as a string)
+```
+
+```forth
+'hello' upper \ gets the upper case version of hello
+```
+
+```forth
+'HELLO' lower \ gets the lower case version of hello
+```
+
+```forth
+'  xx  ' trim \ removes the leading and trailing spaces from the string 
+```
+
+```forth
+'abcd' 'bc' index-of \ finds the substring and returns its index, or -1 if not found
+```
+
+```forth
+'abcxxdepkcxxk' 'xx' 'yyy' replace \ replace all occurances of 'xx' to 'yyy (the substring is a regexp)
+```
+
+```forth
+'af' '123' concat \ concatenates two strings
+```
+
+```forth
+'hello world' ' ' split \ splits the strings into parts by the separator string
+```
+
+```forth
+123 >str \ conversts the number into a string
+```
+
+```forth
+"[ 1 'xx' ] 'a=%d b=%s' format" \ creates a string using the given format by substituting the parts in place of the format characters. 
+```
+
+```forth
+'ab' 3 * \ copies the string n times
+```
 
 
 ## List