# Project Euler Problem 8

• 10-06-2011
Project Euler Problem 8
I'm having a bit of trouble solving this problem. The objective is to find the largest product of five consecutive digits in this 1,000 digit number.
Code:

```#include <stdio.h> int main(void) {         char *num = "73167176531330624919225119674426574742355349194934" "96983520312774506326239578318016984801869478851843" "85861560789112949495459501737958331952853208805511" "12540698747158523863050715693290963295227443043557" "66896648950445244523161731856403098711121722383113" "62229893423380308135336276614282806444486645238749" "30358907296290491560440772390713810515859307960866" "70172427121883998797908792274921901699720888093776" "65727333001053367881220235421809751254540594752243" "52584907711670556013604839586446706324415722155397" "53697817977846174064955149290862569321978468622482" "83972241375657056057490261407972968652414535100474" "82166370484403199890008895243450658541227588666881" "16427171479924442928230863465674813919123162824586" "17866458359124566529476545682848912883142607690042" "24219022671055626321111109370544217506941658960408" "07198403850962455444362981230987879927244284909188" "84580156166097919133875499200524063689912560717606" "05886116467109405077541002256983155200055935729725" "71636269561882670428252483600823257530420752963450";         int i, tmp=1, product = 0, final_product = 0;         for(i = 0; num[i] != NULL; i++)         {                 printf("%i\n", num[i] - '0');                 tmp *= num[i] - '0';                 if((i+1) % 5 == 0)                 {                         printf("------------------------\n");                         product = tmp;                         tmp = 1;                         if(product > final_product)                                 final_product = product;                 }         }         printf("Largest product ------> %i\n", final_product);         return 0; }```
The answer should be 40,824 but I'm getting 31,752. Any ideas where I'm going wrong?
• 10-06-2011
GReaper
Your implementation is loosy. Why don't you use strlen()? That way you'll be able to iterate the digits properly.

EDIT: You mean you solved the former 7? Bravo, keep it up! :cool:
• 10-06-2011
iMalc
Take the first ten digits: 7316717653
You need to calculate all of these:
Code:

```7*3*1*6*7 = ?   3*1*6*7*1 = ?     1*6*7*1*7 = ?       6*7*1*7*6 = ?         7*1*7*6*5 = ?           1*7*6*5*3 = ?```
But you are only calculating the underlined ones.