Advantages of a macro over a function?

Macro gets to see the Compilation environment, so it can expand ___TIME__ __FILE__ #defines. 
It is expanded by the preprocessor. For example, you can’t do this without macros


#define PRINT(EXPR) printf( #EXPR “=%d\n”, EXPR) 


PRINT( 5+6*7 ) // expands into printf(”5+6*7=%d”, 5+6*7 );


You can define your mini language with macros:


#define strequal(A,B) (!strcmp(A,B))


Macros are a necessary evils of life. The purists don’t like them, butwithout it no real work gets done.

What does static variable mean?

there are 3 main uses for the static.
1. If you declare within a function: It retains the value between function calls
2.If it is declared for a function name: By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files
3. Static for global variables: By default we can use the global variables from outside files If it is
static global..that variable is limited to with in the file

"union" Data Type What is the output of the following program? Why?

#include
main() {
typedef union {
int a;
char b[10];
float c;
}
Union;
Union x,y = {100};
x.a = 50;
strcpy(x.b,"hello");
x.c = 21.50;
printf("Union x : %d %s %f n",x.a,x.b,x.c);
printf("Union y : %d %s %f n",y.a,y.b,y.c);
}