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Sunday, April 25, 2010

Converting BASIC Programs to GW-BASIC

Converting BASIC Programs to GW-BASIC

Programs written in a BASIC language other than GW-BASIC 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:


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


Some GW-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 GW-BASIC string concatenation.

In GW-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:


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


E.2 Multiple Assignments

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

10 LET B=C=0

GW-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 GW-BASIC languages use a backslash (\) to separate multiple statements on a line. With GW-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 GW-BASIC languages must be rewritten using FOR-NEXT loops to execute properly.

E.5 FOR-NEXT Loops

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

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