Iban_validation.cpp

/* Test IBAN values:
    HR 15 2340 0093 2109 5545 7
    HR 5023400093102278840
*/

#include <iostream>
#include <string>
#include <algorithm> // needed for remove_if

using namespace std;

bool isValid(string iban)
{
    // trim spaces
    iban.erase( std::remove_if( iban.begin(), iban.end(), ::isspace ), iban.end() );

    // move country code and control number to back
    int len = iban.length();
    string code = iban.substr(4, len - 4) + "1727" + iban.substr(2, 2);


    int n=0, // current operating number
        r=0, // result of division
        l=0; // reminder

    while (code.length() > 0) {
        // append next digit to remider of last division
        string digit = code.substr(0,1);
        n = l*10 + atoi(digit.c_str());

        // drop first digit
        code = code.substr(1, code.length() -1);

        r = n/97;
        l = n%97;
        
        // number is smaller than 97, try appending next digit
        if (r != 0) n=0;
    }

    return (l == 1) ? true : false;
}


int main(int argc, char *argv[])
{
    string iban;
    
    cout << "Input IBAN: ";
    getline(cin, iban);
    
    if (isValid(iban) == true) {
        cout << "Entered IBAN is valid" << endl;
    } else {
        cout << "Entered IBAN is not valid" << endl;
    }

    return 0;
}