CODEWITHSUNDEEP
c
Nilay Arora
Nilay Arora

Reputation: 1

Error Project Euler # 8

I'm working on Problem 8 of Project Euler where I have to find the largest product of 13 consecutive digits from a given 1000 digit number. I stored that number in a text file and then inputted it in my source code. My code compiles and runs, but my answer seems to be incorrect. Can anybody help me figure out where the error is?

Here is my code:

#include <stdio.h>
int main()
{
  int x,ar[1000],i = 0,prod = 0,tmp=1;
  FILE* fp = fopen("file.txt","r");
  if (fp == NULL)
  {
   printf("error");
   return 1;
  }
  while((x = fgetc(fp)) != EOF)
  {
      ar[i] = x;
      i++;
  }
  /*for(int m =0;m<999;m++)
  {
    printf("%d",ar[m]);
  }*/
  for(int j =0;j <= 986;j++)
  {
      for(int k=j;k<j+13;k++)
      {
        tmp = tmp * ar[k];
      }
      if(tmp > prod)
      {
        prod = tmp;
      }
  }
  printf("%i",prod);
  return 0;
}

Upvotes: 0

Views: 167

Answers (2)

starrify
starrify

Reputation: 14751

The product of 13 consecutive digits may exceeds range of int which you're using for tmp. You need data types that supports a wider range. Maybe 64bit ones like unsigned long long would do.

Also as @deviantfan has pointed out, you're reading characters, and '0' as an character is not the same thing as a number 0. Read about ASCII.

Another problem is that the logic of tmp is not correct: you didn't re-initialize it to 1 after each 13 step loop.

EDITED:

Reply to your comment: I suppose in this case the best solution is to read the data as characters, however after that you could convert the ASCII to integer, e.g.:

while((x = fgetc(fp)) != EOF)
{
    // x - '0' does the conversion, 
    // e.g. the expression obtains 0 from '0' - '0', and 5 from '5' - '0'
    ar[i] = x - '0';
    i++;
}

Upvotes: 3

John Bollinger
John Bollinger

Reputation: 180316

You are taking the product of digit chars, not of the digits they represent. '1' != 1.

Upvotes: 2

Related Questions