ANOOB BACKER Technical Blog: May 2006

C Programming - String to Integer (atoi)

Another TechMahindra Interview question. The question was to convert a VALID string into its corresponding integer value.

Post in your comments!

Solution:


int atoi(char *string)
{
    int value=0,sign=1;
    
   if ( !string || !*string ) return 0;
   
   if ( *string == '-' ) {
        sign = -1;
        string++;
   }
   
   while ( *string ) {
         if ( (*string >= '0') && (*string <= '9') ) {
              value = value * 10 + (*string - '0');
         }
         else
             break;
         string++;
   }
   return sign * value;
    
}

Labels: C

Posted by - at 9:36 pm | 1 comments read on

C Programming - Reverse Bits in an Integer

It is supposed to be an 32bit integer.

Solution:


unsigned int
reverse(register unsigned int x)
{
 x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1));
 x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2));
 x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4));
 x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8));
 return((x >> 16) | (x << 16));

}

Labels: C

Posted by - at 7:05 am | 0 comments read on

C Programming - Remove Concequetive Repeting Chars with that Character

What I meant was convert "aaabccddd" to "abcd".

Solution:


#include < stdio.h >
#define STRING "aaabccddd"

int replaceCChars(char *string)
{
    char *dest=string;
    
    while(*string) {
         if ( *string != *(string+1) ) {
                   *dest++ = *string;
         }
         string++;
    }
    *dest = '\0';     
}

int main()
{
    char a[]=STRING;
    printf("Before: %s ",a);
    replaceCChars(a);
    printf("After: %s\n",a);
}

Labels: C

Posted by - at 6:37 am | 3 comments read on

C Programming - Find Perfect Square Between Two Numbers

TechMahindra Interview Question, this is how I did that.

Solution:


#include < stdio.h >
#define START 10
#define STOP 100
int main()
{
    int i=0;
    while( (i*i) < START ) i++;
    while( (i*i) < STOP ) {
           printf("%d ",i*i);
           i++;
    }
}

Labels: C

Posted by - at 6:34 am | 3 comments read on

C Programming - Reverse Words in a String (In-Place)

Another typical interview question!!

Here is the solution that I could think off...Post your comments!!!

Solution:


#include < stdio.h >
#define SENT "Hello I am Here"

int reverse(char *string, char delimiter)
{
    char *src, *dest,*temp=string;
    while( *temp ) {
         if (*temp == delimiter) {
                     temp++;
                     continue;
         }
         src=dest=temp;
         while ( (*(dest+1) != delimiter) && ( *(dest+1) != '\0' ) ) dest++;
         temp=dest+1;
         while( dest > src ) {
                char temp = *dest;
                *dest-- = *src;
                *src++=temp;
         }
    }
}


int main()
{
    char name[] = SENT;
    printf("Before Call: %s\n",name);
    reverse(name,'\0'); /* Reverse Complete Sentence */
    reverse(name,' '); /* Reverse Words */
    printf("After Call: %s\n",name);
    
}

Labels: C

Posted by - at 6:29 am | 4 comments read on