Appendix E

Converting BASIC Programs to GW-BASIC

Programs written in another BASIC language may require some minor adjustments before they can be run. The following sections describe these adjustments.

E.1 String Dimensions

Delete all statements used to declare the length of strings. A statement such as the following:

DIM A$(I,J)

which dimensions a string array for J elements of length I, should be converted to the following statement:

DIM A$(J)

Some BASIC languages use a comma or ampersand (&) for string concatenation. Each of these must be changed to a plus sign (+), which is the operator for BASIC string concatenation.

In BASIC, the MID$, RIGHT$, and LEFT$ functions are used to take substrings of strings. Forms such as A$(I) to access the Ith character in A$, or A$(I,J) to take a substring of A$ from position I to position J, must be changed as follows:

Other BASIC	BASIC
X$=A$(I)	X$=MID$(A$,I,1)
X$=A$(I,J)	X$=MID$(A$,I,J-I+1)

If the substring reference is on the left side of an assignment, and X$ is used to replace characters in A$, convert as follows:

Other BASIC	BASIC
A$(I)=X$	MID$(A$,I,1)=X$
A$(I,J)=X$	MID$(A$,I,J-I+1)=X$

E.2 Multiple Assignments

Some BASIC languages allow statements of the following form to set B and C equal to zero:

10 LET B=C=0

BASIC would interpret the second equal sign as a logical operator and set B equal to -1 if C equaled 0. Convert this statement to two assignment statements:

10 C=0: B=0

E.3 Multiple Statements

Some BASIC languages use a backslash () to separate multiple statements on a line. With BASIC, be sure all elements on a line are separated by a colon (:).

E.4 MAT Functions

Programs using the MAT functions available in some BASIC languages must be rewritten using FOR...NEXT loops to execute properly.

E.5 FOR-NEXT Loops

Some BASIC languages will always execute a FOR...NEXT loop once, regardless of the limits. BASIC checks the limits first and does not execute the loop if past limits.