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Additional Capabilities Keyboard Sound Graphics Concepts Screen (text) Screen (drawing) Gaming (sprites) Event Trapping Errors System Calls

String Functions Summary
One of QBasic's strengths is in the manipulation of strings, offering over 20 different built-in string functions. The functions can be categorized roughly into four areas:

Case-Conversion	ucase$, lcase$
String Variable Properties..	val len
Single Character Function	asc, chr$
Truncate Strings	left$, right$
Remove Spaces	ltrim$, rtrim$
Find/Replace	mid$, instr
Justification	lset, rset
Return Repetitive Strings	space$, string$
Convert Numbers to String	cvi, cvl, cvs, cvd
Convert Numbers to String	str$, mkd$, mki$, mks$, mkl$
Assignment	let, swap, clear

String Function Reference
Here's a quick reference of the available string functions, in alphabetical order. The functions are very simple to use.

• asc - returns ASCII code for 1st character in a string

      result$ = asc("hello")      # returns ASCII of "h", which is 104
      

• chr$ - returns characters corresponding to specified ASCII code

      result$ = chr$ (104)        # returns "h"
      

• clear - closes all files, clears all common variables, reset values of all strings/numbers.

      clear                     # no arguments required
      

• cvi - convert integer to string

      result$ = cvi(var%)      # result$ = string value of var$
      result$ = cvi(24)        # result$ = "24"
      

• cvl - convert long integer to string

      result$ = cvl(var&)      # result$ = string value of var&
      result$ = cvl(71224)        # result$ = "71224"
      

• cvs - convert single to string

      result$ = cvs(var!)      # result$ = string value of var!
      result$ = cvs(1.224)        # result$ = "1.224"
      

• cvd - convert double to string

      result$ = cvd(var#)      # result$ = string value of var#
      result$ = cvd(24.78882)        # result$ = "24.78882"
      

• instr - returns position of one string within another string

      result = instr (StartPos%, StringToSearch$, StringToFind$)
      result = instr (1, "abcdefg", "de")  # returns 4
      

  Note: First character is position 1. StartPos% is optional (default is position 1).

• lcase$ - converts string to all lowercase letters

      result$ = lcase$ ("HELP Me")      # returns "help me"
      

• left$ - returns specified leftmost number of characters

      result$ = left$("Hello",2)        # returns "He"
      

• len - desc

      result = len ("hello")     # returns 5
      x$ = "dog"
      result = len(x$)           # returns 3
      

• let - assigns value to a variable

      let result = 5
      

• lset - left justifies a smaller string within a larger string of spaces

      buffer$ = "          "        # ten spaces
      lset buffer$ = "dog"          # buffer$ contains "dog       "
      

  Note: The original content of buffer$ is replaced with spaces before placing the smaller string.

• ltrim$ - removes leading spaces from a string

      result$ = ltrim$("  mydog")        # returns "mydog"
      

• mid$ - returns or replaces part of a string

      result$ = mid$(StringToSearch$, StartPos%, Length%)  
      result$ = mid$("abc123def", 1, 3)       # returns "abc"
      result$ = mid$("abc123def", 3, 3)       # returns "c12"
  
      mid$(EditString$, StartPos%, Length%) = ReplacementString$
      var$ = "my dog is nice"
      mid$(var$, 4, 3) = "cat"      # var$ = "my cat is nice"
      

  Length is optional in both cases. If omitted, mid$ returns or replaces all characters to the right of the start position.

• mkd$ - convert double to a string

      result$ = mkd$(var#)        # result is string version of var#
      result$ = mkd$(1.234)       # result is "1.234"
      

• mki$ - convert integer to a string

      result$ = mkd$(var%)        # result is string version of var%
      result$ = mkd$(12)          # result is "12"
      

• mkl$ - convert long integer to a string

      result$ = mkl$(var&)        # result is string version of var&
      result$ = mkl$&(7423234)    # result is "7423234"
      

• mkds - convert single to a string

      result$ = mks$(var!)        # result is string version of var!
      result$ = mks$(1.234)       # result is "1.234"
      

• left$ - returns specified rightmost number of characters

      result$ = right$("Hello",2)        # returns "lo"
      

• rset - right justifies a smaller string within a larger string of spaces

      buffer$ = "          "     # ten spaces
      rset buffer$ = "dog"       # buffer$ contains "       dog"
      

  Note: The original content of buffer$ is replaced with spaces before placing the smaller string.

• rtrim$ - removes trailing spaces from a string

      result$ = rtrim$("mycat  ")        # returns "mycat"
      

• space$ - returns a string of spaces of a specified length

      result$ = space$(5)       # returns "     ", which is 5 spaces
      

• str$ - returns a string representation of a number

      result$ = str$(12)           # returns "12"
      result$ = str$(1.342)        # returns "1.342)
      

• string$ - returns string of a repetitive character

      result$ = string$(Repititions%, CharacterToRepeat$)
      result$ = string$(5,"a")    # returns "aaaaa" 
      result$ = string$(5,66)     # returns "BBBBB" - ASCII 66 is "B"
      

  Note: If CharacterToRepeat is more than one character, only the first character is repeated.

• swap - exchange values of two variables

      a$ = "a" : b$ = "b"   # set test values
      swap a$, b$           # a$ = "b" and b$ = "a" (values swapped)
      

• ucase$ - converts string to all uppercase letters

      result$ = lcase$ ("Help Me")      # returns "HELP ME"
      

• val - converts a string to a number

      result = val("12.3")           # returns 12.3
      result = val("abc")            # returns 0 
      result = val("12ab")           # returns 12
      

Missing Functions
I purposely left out functions related to Microsoft-Binary-Format (MBF) numeric formats, which were supported in earlier versions of Basic. The missing functions are MKSMBF$, MKDMBF$, CVSMBF and CVDMBF.

If you have suggestions or corrections, please let me know.