title: Project Euler 8 in C, working with 4 digits and fails for 13 digits?
body: <p>I have coded the problem in C. When I run the code to find the solution for the four adjacent digits in the 1000-digit number that have the greatest product I get the correct answer. But with the 13 adjacent digits I am always getting the wrong answer (2039787520), can someone point it out where I am wrong?</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;stdint.h&gt;
  #include &lt;inttypes.h&gt;
  
  //Storing the 1000 digits
  char number_array[] =   "73167176531330624919225119674426574742355349194934"
                          "96983520312774506326239578318016984801869478851843"
                          "85861560789112949495459501737958331952853208805511"
                          "12540698747158523863050715693290963295227443043557"
                          "66896648950445244523161731856403098711121722383113"
                          "62229893423380308135336276614282806444486645238749"
                          "30358907296290491560440772390713810515859307960866"
                          "70172427121883998797908792274921901699720888093776"
                          "65727333001053367881220235421809751254540594752243"
                          "52584907711670556013604839586446706324415722155397"
                          "53697817977846174064955149290862569321978468622482"
                          "83972241375657056057490261407972968652414535100474"
                          "82166370484403199890008895243450658541227588666881"
                          "16427171479924442928230863465674813919123162824586"
                          "17866458359124566529476545682848912883142607690042"
                          "24219022671055626321111109370544217506941658960408"
                          "07198403850962455444362981230987879927244284909188"
                          "84580156166097919133875499200524063689912560717606"
                          "05886116467109405077541002256983155200055935729725"
                          "71636269561882670428252483600823257530420752963450";
  
  int main(void){
    int length = sizeof(number_array);
    int64_t max_product = 0;
    int i, j;
  
     for( i = 0; i &lt;= length - 13; i++){
  
       int64_t  product = 1;
  
        //Going through 13 consecutive digits for each digit in the char 
         array
        for(j = 0; j &lt; 13; j++){
          printf("product -- &gt; %d and number -- &gt; %d\n",product ,
          (number_array[i+j] - 0x30));
  
          // finding the product
          product = product * (number_array[i + j] - 0x30);
  
        //if product is zero skipping the process
          if(product == 0){break;}
        }
  
       printf("product -- &gt; %I64d\n", product);
  
       //checking for the max product
       if(product &gt; max_product){
         max_product = product;
       }
  
     }
  
    printf("max_product -- &gt; %I64d\n", max_product);
  }
  
  `
  </code></pre>