C Interview Programs – Part 01

I this post we have provided part 1 of the C programs most commonly asked in interview along with answers. We recommend you to try to answer the questions, before referring to the given answer. If you find any mistake or a better alternate solution we are happy to see your suggestions and comments

1. Write function to reverse linked list

void Reverse(Node_t **head)
{
   Node_t *cur = *head;
   Node_t *prev = NULL;
   Node_t *next = NULL;
   while(cur)
   {
      next = cur->next;
      cur->next = prev;
      prev = cur;
      cur = next;
   }
   *head = prev;
   return;
}

Reverse(&head);

2. Write function to reverse linked list using recursion

Node_t * Reverse(Node_t *head, Node_t *prev)
{
   Node_t *last = 0;
   if(0 == head) return prev;
   last = Reverse(head->next, head);
   head->next = prev;
   return last;
}

3. Write a function to insert in a doubly linked list

void InsertAfter(Node_t *cur, Node_t *new)
{
   new->next = cur->next;
   cur->next = new;
   new->prev = cur;
   new->next->prev = new;
}

4. Write the implementation of strlen() function

size_t strlen(const char *str)
{
   size_t len = 0;
   while(str[len++]);
   return len;
}

5. Write the implementation of strcpy() function

char * strcpy(char *dst, const char *src)
{
   char *itr = dst;
   while(*itr++ = *src++);
   return dst;
}

6. Write the implmentation of strncpy() function

char * strncpy(char *dst, const char *src, size_t len)
{
   char *itr = dst;
   while(len-- && (*itr++ = *src++));
   return dst;
}

7. Write the implementation of strcat() fucntion

char * strcat(char *dst, const char *src)
{
   char *end = dst;
   while(*end) end++;
   while(*end++ = *src++);
   return dst;
}

8. Write the implementation of strncat() function

char * strncat(char *dst, const char *src, size_t len)
{
   char *end = dst;
   while(*end) end++;
   while(*end++ = *src++ && len--)
   *end = 0;
   return dst;
}

9. Write the implementation of strchr() function

char * strchr(char *src, const char ch)
{
   while(*src)
   {
      if(*src == ch)
         return src;
      else src++;
   }
   return NULL;
}

10. Write the implementation of strrchr() function

char * strrchr(char *str, const char ch)
{
   char *end = str;
   while(*end) end++;
   while(*--end)
      if(*end == ch)
         return end;
   return NULL;
}