8-bit MicrocontrollersのトピックDeclaration type

Declaration type

DavidoBG — Thu, 04 Jun 2009 17:06:08 GMT

I don't understand why theses following operations could be OK or NOK when i run program with simulator.

void main()

{

long number;

number = 1000*33; //The result is -32536

}

void main()

{

long number;

number = 1000*3.3*10; //The result is 33000

}

Do you have any explanations? In fact i would like do a big operation what king of type number declaration i will use?

Thanks a lot

david

Re: Declaration type

CrasyCat — Thu, 04 Jun 2009 21:45:17 GMT

Hello

According to the standard an ANSI C compiler will evaluate expression like 1000*33 on an int (16-bit) value and then result will be signed extended to long.

You need to tell the compiler the expression should be evaluated on 32-bit value.

In this purpose use the L prefix in one of the operant.

Your expression should be written 1000L * 33

This is compliant with ANSI C language definition.

CrasyCat