Select certain number

[uglybetty]

Hello,

Lets say A is equal to 12345678912345. How can I select the third and fourth number in the numbers as input in B. And the eighth and ninth number as input in C. And B and C will be combined to become D. Can someone help me? Thank u.

[Thomas1965]

Easiest is to convert A to a string, extract the wanted digits, convert them to an int and add them together.

#include <iostream>
#include <string>
#include <cctype>

using std::string;
using std::cout;
using std::cin;
using std::to_string;

/*
Lets say A is equal to 12345678912345. 
How can I select the third and fourth number in the numbers as input in B. 
And the eighth and ninth number as input in C. 
And B and C will be combined to become D.
*/
int main()
{
  long long A = 12345678912345;

  string s = to_string(A);
  int B = (s[2] - '0') * 10 + (s[3] - '0'); // * has higher priority than -
  int C = (s[7] - '0') * 10 + (s[8] - '0');
  int D = B * 100 + C;

  cout << "B = " << B << "\nC = " << C << "\nD = " << D << "\n\n"; 
}

Output:

B = 34
C = 89
D = 3489

[lastchance]

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

using INT = unsigned long long;

vector<int> digitise( INT n )
{
   vector<int> digits;
   for ( ; n; n /= 10 ) digits.push_back( n % 10 );
   reverse( digits.begin(), digits.end() );
   return digits;
}


int main()
{
   INT A, B, C, D;
// cout << "Input A: ";   cin >> A;
   A = 12345678912345;

   vector<int> digits = digitise( A );
   if ( digits.size() < 9 )
   {
      cout << "Number not large enough";
      return 1;
   }
   else
   {
      B = 10 * digits[2] + digits[3];
      C = 10 * digits[7] + digits[8];
      D = 100 * B + C;       // Is this what you meant by "combined"?
//    D = B + C;             // Or just add them up?
   }
   cout << "B, C, D = " << B << ", " << C << ", " << D << '\n';
}

You could also do it with substrings:

#include <iostream>
#include <string>
using namespace std;

using INT = unsigned long long;


int main()
{
   INT A, B, C, D;
// cout << "Input A: ";   cin >> A;
   A = 12345678912345;

   string sA = to_string( A );
   if ( sA.size() < 9 )
   {
      cout << "Number not large enough";
      return 1;
   }
   else
   {
      B = stoi( sA.substr( 2, 2 ) );
      C = stoi( sA.substr( 7, 2 ) );
      D = 100 * B + C;
   }
   cout << "B, C, D = " << B << ", " << C << ", " << D << '\n';
}

or with a sledgehammer:

#include <iostream>
#include <cassert>
using namespace std;

using INT = unsigned long long;

int main()
{
   INT A, B, C, D, power = 1;
// cout << "Input A: ";   cin >> A;
   A = 12345678912345;   

   while ( power <= A ) power *= 10;   assert( power >= 1000000000 );

   B = ( A / ( power / 10000      ) ) % 100;
   C = ( A / ( power / 1000000000 ) ) % 100;
   D = 100 * B + C;
   cout << "B, C, D = " << B << ", " << C << ", " << D << '\n';
}

B, C, D = 34, 89, 3489

[uglybetty]

Thanks @Thomas1965 and @lastchance for your help. It works well. :)