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  1. #include<iostream> 
  2. #include<math.h>
  3. #include<iomanip>
  4. #include <string>
  5. #include<algorithm>
  6. #include <vector>
  7. using namespace std;
  8.  
  9. long long fact(int m) {
  10.     long long factorial = 1;
  11.     for (int i = 1;i <= m;i++) {
  12.         factorial *= i;
  13.     }
  14.     return  factorial;
  15. }
  16. void fast()
  17. {
  18.     ios_base::sync_with_stdio(0);
  19.     cin.tie(0);
  20.     cout.tie(0);
  21. }
  22.  
  23. int main()
  24. {
  25.     fast();
  26.  
  27.     int n;
  28.     cin >> n;
  29.  
  30.     int count = 1;
  31.         long long factorial = 1;
  32.  
  33.         for (int i = 1;i <= n;i++) {
  34.             factorial *= i;
  35.  
  36.             while (factorial >= 10) {
  37.                 count++;
  38.                 factorial /= 10;
  39.             }
  40.         }
  41.         cout << "Number of digits of " << n << "! is " << count;
  42.  
  43.     return 0;
  44. }
  45.  
Success #stdin #stdout 0s 5316KB
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stdin
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Standard input is empty
stdout
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Number of digits of 21944! is 82910
https://ideone.com/EZHm3s
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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