Home Questions Search Forum Contact Guest Book Polls! Got a Question?
PREV Write your own .... NEXT   (20 / 301)     Write your own C program to implement the atoi() function The prototype of the atoi() function is ... int atoi(const char *string); Here is a C program which explains a different way of coding the atoi() function in the C language. #include<stdio.h> int myatoi(const char *string); int main(int argc, char* argv[]) {   printf("\n%d\n", myatoi("1998"));    getch();   return(0); } int myatoi(const char *string) {     int i;     i=0;     while(*string)     {         i=(i<<3) + (i<<1) + (*string - '0');         string++;         // Dont increment i!     }     return(i); } Try working it out with a small string like "1998", you will find out it does work!. Ofcourse, there is also the trivial method .... "1998" == 8 + (10 * 9) + (100 * 9) + (1 * 1000) = 1998  This can be done either by going from right to left or left to right in the string One solution is given below int myatoi(const char* string)  {   int value = 0;      if (string)   {     while (*string && (*string <= '9' && *string >= '0'))      {       value = (value * 10) + (*string - '0');       string++;     }   }    return value;  }  Note that these functions have no error handling incorporated in them (what happens if someone passes non-numeric data (say "1A998"), or negative numeric strings (say "-1998")). I leave it up to you to add these cases. The essense is to understand the core logic first. PREV COMMENTS                                  INDEX                                  PRINT NEXT Last updated: November 3, 2005 www.cracktheinterview.com - Your destination for the most common IT interview questions, answers, frequently asked interview questions (FAQ), C Programs, C Datastructures for technical interviews conducted by the top IT companies around the world!