C51: Using #IF to Test Conditions

Information in this article applies to:

• C251 Version 2.14 and later
• C51 Version 5.50 and later

SYMPTOMS

In A51, I can do the following:

$if (CPU=1 OR DISP=3)

with 2 or more conditions. However, in C51 I could not find a way to do this. The following code:

#if CPU==1 OR DISP==2

gives me an error message. What's wrong?

CAUSE

The #if preprocessor directive in C expects C operators to be used.

RESOLUTION

Try using the logical or operator ('||') as shown in the following.

#if CPU==1 || DISP==2

That should work.

MORE INFORMATION

• Refer to #if in the Cx51 User's Guide.

Refer to a good C manual for more information about how to use the #if preprocessor directive.

Last Reviewed: Thursday, February 25, 2021