What will happen in these three cases?

if(a=0){
//somecode
}
if (a==0){
//do something
}
if (a===0){
//do something
}

 

What are x, y, y, u

#define Atype int*
typedef int *p;
p x, z;
Atype y, u;

Answer: x and z are pointers to int. y is a pointer to int but u is just an integer variable

 

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

 

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, but without it no real work gets done.

 

What are the differences between malloc() and calloc()?

There are 2 differences.
First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable).
Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.