in BASIC ROM:
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Remark: This article describes the BASIC command ASC in BASIC V2 at the Commodore 64.
Type: Numerical Function General Programming-Syntax: ASC(<String>)
The ASC keyword takes the first char of a string and maps it to the numeric index of the Commodore ASCII-table. This value can be converted back to the character by using the CHR$ function.
Evaluation of an empty string ("") results in the BASIC-error ?ILLEGAL QUANTITY ERROR. Since BASIC 7.0 this has been fixed and ASC("") returns the value 0. See Examples section for common usage.
If the operand doesn't evaluate to a string the BASIC error ?TYPE MISMATCH ERROR appears. If no operand is provided the error message ?SYNTAX ERROR shows up.
Examples[edit | edit source]
Parameter[edit | edit source]
PRINT ASC("A") 65 PRINT ASC("ABC") 65 PRINT ASC("") ?ILLEGAL QUANTITY ERROR PRINT ASC ?SYNTAX ERROR PRINT ASC(1) ?TYPE MISMATCH ERROR
BASIC 7.0[edit | edit source]
PRINT ASC("") 0
No error condition anymore!
Common usage[edit | edit source]
In a program the efficient way to use the ASC function is (in regard to cope with the special case "empty string") is
10 Z$=CHR$(0) ... 1000 A=ASC(A$+Z$)
The variable definition speeds the thing up (avoiding the evaluation of the CHR$ function and its parameter). The definition of Z$ should be placed at the very beginning to ensure a fast access to this variable.
Other variants like
IF A$="" THEN A$=CHR$(.) A=ASC(A$)
and so on are either impractical or take to much code space. However they are always slower.
Read a sequential file bytewise[edit | edit source]
10 Z$=CHR$(0) 100 OPEN 2,8,3,"FILENAME,S,R" 110 FOR S=0 TO 1 120 GET#2,A$ 130 A=ASC(A$+Z$) 140 S=ABS(ST) 150 PRINT A; 160 NEXT S 170 CLOSE 2 ...
The command GET# needs special treatment. If a CHR$(0) is read the result is an empty string, which can be fixed as follows:
- if A$ is empty, concatenate string Z$ (contains CHR$(0)) which results in the final string containing CHR$(0).
- if A$ is not empty the concatenation doesn't change anything because ASC() takes only the first character.
The recommendation is to use a variable for CHR$(0), see above Common Usage.
The FOR-NEXT loop has its advantage to speed things up and terminates as soon the status (ST system-variable) return a value not equal 0 (this happens on end-of-file or error condition) which is achieved by manipulating the FOR-NEXT variable S.
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