C Interview Questions Set-3

11. What is C standard?
The latest C standard is ISO/IEC 9899:2011, also known as C11 as the final draft was published in 2011. Before C11, there was C99. The C11 final draft is available here. See this for complete history of C standards.

12. What is the output of the following program? Why?

#include<stdio.h>

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);

}

13. 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 

14. What are the 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.

15. 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.