IT Interview Questions

Implementing itoa function is a popular interview question. Here’s one implementation from SAP.

char *itoa(int value)
{
int count,                   /* number of characters in string       */
i,                       /* loop control variable                */
sign;                    /* determine if the value is negative   */
char *ptr,                   /* temporary pointer, index into string */
*string,                /* return value                         */
*temp;                  /* temporary string array               */

count = 0;
if ((sign = value) < 0) /* assign value to sign, if negative */
{ /* keep track and invert value */
value = -value;
count++; /* increment count */
}

/* allocate INTSIZE plus 2 bytes (sign and NULL) */
temp = (char *) malloc(INTSIZE + 2);
if (temp == NULL)
{
return(NULL);
}
memset(temp,’\0′, INTSIZE + 2);

string = (char *) malloc(INTSIZE + 2);
if (string == NULL)
{
return(NULL);
}
memset(string,’\0′, INTSIZE + 2);
ptr = string; /* set temporary ptr to string */

/*——————————————————————–+
| NOTE: This process reverses the order of an integer, ie: |
| value = -1234 equates to: char [4321-] |
| Reorder the values using for {} loop below |
+——————————————————————–*/
do {
*temp++ = value % 10 + ‘0′; /* obtain modulus and or with ‘0′ */
count++; /* increment count, track iterations*/
} while (( value /= 10) >0);

if (sign < 0) /* add ‘-’ when sign is negative */
*temp++ = ‘-’;

*temp– = ‘\0′; /* ensure null terminated and point */
/* to last char in array */

/*——————————————————————–+
| reorder the resulting char *string: |
| temp - points to the last char in the temporary array |
| ptr - points to the first element in the string array |
+——————————————————————–*/
for (i = 0; i < count; i++, temp–, ptr++)
{
memcpy(ptr,temp,sizeof(char));
}

return(string);