linux macro in C

int main(void)
{ 
 int linux = 5;
 printf("%d",linux);
 return 0;
}

When u compile this application using gcc in linux, you will get compilation error, this is because linux is a macro which is defined to 1 You can look this by stopping at the preprocessing stage gcc -E test.c will stop this at the preprocessing stage.

int main(void)
{
 int 1 = 5;
 printf("%d",1);
 return 0;
}

You can see the linux is expanded to 1 in the preprocessing stage and hence the error.