About Conditional Inclusion

[Huangsyx]

#include <stdio.h>

int main(void)
{
int a = 1;

#if 1 == a
puts("Success");
#else
puts("Failure");
#endif

return 0;
}

I've Compile this code in Visual C++ 6.0 and MingW.
It' Ok, but puts"Failure".
Why?
Alsoly, I've Compier this code in Turbo C 2.0. The TC(Turbo C)2.0 report an Error."Constant expression required in function main".

What the definination of "constant of expression"?

I am a beginner.

 

[Ben Pfaff]

int a = 1;

#if 1 == a
puts("Success");
#else
puts("Failure");
#endif

This does not do what you think it does. Variables are not
visible in preprocessor expressions. In preprocessor
expressions, undefined names are silently replaced by 0. So "#if
1 == a" is equivalent to "#if 1 == 0".

I've Compile this code in Visual C++ 6.0 and MingW.
It' Ok, but puts"Failure".
Why?

This should be clear.

Alsoly, I've Compier this code in Turbo C 2.0. The TC(Turbo
C)2.0 report an Error."Constant expression required in function
main".

Turbo C 2.0 was released late in 1988. I doubt that it is fully
ANSI C compliant. Use some other compiler.