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  1. #include <stdio.h>
  2.  
  3. #define MAX_DIGITS 200  // Enough space for 50!
  4.  
  5. // Multiplies the big number (stored in result as digits in reverse order)
  6. // by the given factor. The current size of the number is pointed to by result_size.
  7. void multiply(int factor, int result[], int *result_size) {
  8.     int carry = 0;
  9.     for (int i = 0; i < *result_size; i++) {
  10.         int prod = result[i] * factor + carry;
  11.         result[i] = prod % 10;
  12.         carry = prod / 10;
  13.     }
  14.     while (carry) {
  15.         result[*result_size] = carry % 10;
  16.         carry /= 10;
  17.         (*result_size)++;
  18.     }
  19. }
  20.  
  21. // Computes factorial(n) using an iterative approach.
  22. void factorial(int n) {
  23.     // The big number is stored in an array, with the least-significant digit at index 0.
  24.     int result[MAX_DIGITS] = {0};
  25.     int result_size = 1;
  26.     result[0] = 1; // Initialize with 1
  27.  
  28.     for (int i = 2; i <= n; i++) {
  29.         multiply(i, result, &result_size);
  30.     }
  31.  
  32.     // Print the big number in the correct order (most-significant digit first)
  33.     for (int i = result_size - 1; i >= 0; i--) {
  34.         printf("%d", result[i]);
  35.     }
  36.     printf("\n");
  37. }
  38.  
  39. int main(void) {
  40.     factorial(50);
  41.     return 0;
  42. }
  43.  
Success #stdin #stdout 0.01s 5288KB
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Standard input is empty
stdout
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30414093201713378043612608166064768844377641568960512000000000000
https://ideone.com/WWESv6
language:
C99 (gcc 8.3)
created:
3 days ago
visibility:
public

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