Recursive Format numbers with commas

 You may also like to use the enclosed snippet that demo's a way to validate if a C++ string represents an integer.

// validates string 's' passed in and extracts a front sign (if there) into char var 'sign'
bool isInt( string& s, char& sign ); // Note: string without a 'sign' is returned


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

// Recursive method of adding commas to numbers as C++ strings ...
// s is string passed in, i is index of next char to add to new string,
// ns is new string returned by ref. with commas inserted ...
void addCommas( const string& s, int i, string& ns )
{
    int j, k = 0;
    for(j = i; j >= 0 && k < 3; --j, k++ )
    {
        ns = s[j] + ns; // new char is added to front of ns
        if( j > 0 && k == 2) ns = "," + ns;
    }
    if( i-3 >= 0 ) addCommas( s, i-3, ns );
}


// For BEGINNING COMPUTER PROGRAMMING using HLA, Python, C/C++
// http://developers-heaven.net/forum/index.php/topic,46.0.html


// validates string s passed in and extracts a front sign into char var 'sign'
bool isInt( string& s, char& sign ) // Note: string without a 'sign' is returned
{
    sign = 0; // default sign  ... i.e no sign ...

    // first ... strip off all trailing whitespace ...
    int j = 0,
        len = s.length();
    while( s[len-1-j] == ' ' || s[len-1-j] == '\t' ) ++j;
    s.erase(len-j); // i.e. erase all j trailing whitespace ...

    if( s == "" ) return false; // test here for empty string ...

    // if reach here ... some non-ws exits ... so now ...
    // skip over all leading whitespace
    j = 0;
    while( s[j] == ' ' || s[j] == '\t' ) ++j;
    s = s.substr(j); // i.e. skip over j leading whitesapce char's

    // now check for pos or neg sign character ... (in front of other char's)
    if(  s.length() > 1  &&  (s[0] == '-' || s[0] == '+') )
    {
        sign = s[0];
        s.erase(0,1);   // or ... could use s = s.substr(1);
    }

    // handle special cases of '-0'  ... leading  ... or all zero's ...
    len = s.length(); // update len ...
    for( int i = 0; i < len-1; ++i ) // i < len-1 leaves last zero in place ...
    {
        if( s[0] == '0' ) s.erase(0,1);
        else break; // since a non-zero char was found ...
    }
    if( s == "0" ) { sign = 0; return true; }

    len = s.length(); // ok ... get updated length of string & test digits ...
    for( int i = 0; i < len; ++i )
    {
        if( s[i] < '0' || s[i] > '9' ) return false; // since non 0..9 found
    }
    return true;
}

// defaults to ... 'Yes more' ... unless 'n' or 'N' was entered ...
bool more() // returns true unless 'n' or 'N' entered, then and only then, false
{
    cout << "\nMore y/n ? " << flush;
    int reply = cin.get();
    cin.sync(); // 'flush' cin stream ...
    return reply != 'n' && reply != 'N' ;
}



int main()
{
    for( ; ; )
    {
        string str, nstr;  // set to "" by class string default constructor
        cout << "Please enter an integer of any size : " << flush;
        getline ( cin, str );
        char sign;
        if( !isInt( str, sign ) ) { cout << "Error! ... "; continue; }
       
        addCommas( str, str.length()-1, nstr );
       
        // show sign only if we had a signed integer ... i.e if sign != 0
        if( sign ) cout << sign;
        cout << nstr << " with " << nstr.length() - nstr.length()/4
             << " significant digit(s)." << endl;
        if( !more() ) break;
    }
}

Artikel Terkait: