?TYPE MISMATCH ERROR
Commodore Commodore 64
Severity: MinorWhat it means
?TYPE MISMATCH ERROR means you used a string where a number was expected, or a number where a string was expected.
For example: LET A = "HELLO" + 5 mixes a string and a number, which BASIC cannot handle.
Affected Models
- Commodore 64
- Commodore 64C
- Commodore 128 (C64 mode)
- VICE emulator (C64)
Common Causes
- Adding a string variable to a numeric variable (e.g. A$ + B where B is numeric)
- Passing a string to a function that expects a number (e.g. SQR(A$))
- Passing a number to a string function (e.g. LEFT$(5, 2) instead of LEFT$(A$, 2))
- Using = to compare a string variable to a number
- INPUT storing a string into a numeric variable (user typed letters when number was expected)
How to Fix It
-
Check whether your variables are numeric or string types.
In C64 BASIC, variable names ending in $ are strings (A$, NAME$).
All others are numeric (A, X, SCORE).
You cannot mix them in expressions. -
Use VAL() to convert a string to a number when needed.
If A$ = "42" and you need to do arithmetic: use VAL(A$) instead of A$ directly.
VAL("42") returns the number 42. -
Use STR$() to convert a number to a string when needed.
If you need to join a number into a string: PRINT "SCORE: " + STR$(SCORE) works because STR$(SCORE) converts the number to a string.
-
When using INPUT, validate what the user typed before using it as a number.
If your program does INPUT A and the user types HELLO, A contains a string value that will cause TYPE MISMATCH if used in arithmetic.
Add a check or use INPUT A$ then convert with VAL().
Frequently Asked Questions
Why does C64 BASIC use $ to mark string variables?
This convention comes from Microsoft BASIC, which Commodore licensed for the C64.
The $ suffix is a shorthand way of telling the interpreter that the variable holds text rather than a number — no type declaration needed.
Can I store a number like 42 in a string variable on the C64?
Yes.
A$ = "42" stores the text 42 in a string variable.
But you cannot do arithmetic on it directly — use VAL(A$) to get the numeric value first.