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C Exercises: Find the thirteen adjacent digits in the 1000-digit number that have the greatest product

C Programming Practice: Exercise-24 with Solution

The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450.
Write a C programming to find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

C Code:

#include <stdio.h>
int main(void)
{
  char user_str[] =
    "73167176531330624919225119674426574742355349194934"
    "96983520312774506326239578318016984801869478851843"
    "85861560789112949495459501737958331952853208805511"
    "12540698747158523863050715693290963295227443043557"
    "66896648950445244523161731856403098711121722383113"
    "62229893423380308135336276614282806444486645238749"
    "30358907296290491560440772390713810515859307960866"
    "70172427121883998797908792274921901699720888093776"
    "65727333001053367881220235421809751254540594752243"
    "52584907711670556013604839586446706324415722155397"
    "53697817977846174064955149290862569321978468622482"
    "83972241375657056057490261407972968652414535100474"
    "82166370484403199890008895243450658541227588666881"
    "16427171479924442928230863465674813919123162824586"
    "17866458359124566529476545682848912883142607690042"
    "24219022671055626321111109370544217506941658960408"
    "07198403850962455444362981230987879927244284909188"
    "84580156166097919133875499200524063689912560717606"
    "05886116467109405077541002256983155200055935729725"
    "71636269561882670428252483600823257530420752963450";
  size_t len = sizeof user_str - 1;
  size_t i;
  unsigned max_val = 0;
  for (i = 0; i < len-4; i++) {
    unsigned p = 1;
    size_t j;
    for (j = 0; j < 5; j++) {
      p *= (unsigned)(user_str[i+j]-'0');
    }
    if (p > max_val) {
      max_val = p;
    }
  }
  printf("%u\n", max_val);
  return 0;
}

Sample Output:

40824

Flowchart:

C Programming Flowchart: Find the thirteen adjacent digits in the 1000-digit number that have the greatest product.

C Programming Code Editor:

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Previous: Write a C programming to get the 1001st prime number?.
Next: Write a C programming to find the product xyz.

What is the difficulty level of this exercise?

C Programming: Tips of the Day

C Programming - Why do all the C files written by my lecturer start with a single # on the first line?

In the very early days of pre-standardised C, if you wanted to invoke the preprocessor, then you had to write a # as the first thing in the first line of a source file. Writing only a # at the top of the file affords flexibility in the placement of the other preprocessor directives.

From an original C draft by the great Dennis Ritchie himself:

12. Compiler control lines

[...] In order to cause [the] preprocessor to be invoked, it is necessary that the very first line of the program begin with #. Since null lines are ignored by the preprocessor, this line need contain no other information.

That document makes for great reading (and allowed me to jump on this question like a mad cat).

I suspect it's the lecturer simply being sentimental - it hasn't been required certainly since ANSI C.

Ref : https://bit.ly/2Mb8OVZ