Prevod z dvojkove soustavy

int main()
{
    string s = "101011";
    int len = s.length();
    int v = 0; // vysledek
 
    for (int i = 0; i < len; i++)
    {
        char c = s[i];
        v = 2 * v; // posunout, pridat na konec nulu
        if (c == '1')
            v = v + 1;
    }
 
    cout << s << " ... " << v << endl;

int main()
{
    int v = 22; // vstup
    string s = ""; // vystupni text
 
    int n = v;
    while (n > 0)
    {
        if (n % 2 == 0)
            s = "0" + s;
        else
            s = "1" + s;
 
        n = n / 2;
    }
 
    if (v == 0) s = "0"; // pro nulu na vstupu byl vysledkem prazdny retezec
 
    cout << v << " ... " << s << endl;
}

Prevod do dvojkove soustavy

#include <iostream>
using namespace std;
 
int main()
{
    string s = "Ff";
    int len = s.length();
    int v = 0; // vysledek
    int base = 16; // zaklad ciselne soustavy
 
    for (int i = 0; i < len; i++)
    {
        char c = s[i];
        v = v * base; // posunout, pridat na konec nulu
        int d = 99;
        if (c >= '0' && c <= '9')
        {
            d = c - '0';
        }
        else if (c >= 'A' && c <= 'Z')
        {
            d = c - 'A' + 10;
        }
        else if (c >= 'a' && c <= 'z')
        {
            d = c - 'a' + 10;
        }
        if (d >= base) cout << "spatna cislice " << c << endl;
        v = v + d;
    }
 
    cout << s << " ... " << v << endl;
}

#include <iostream>
using namespace std;
 
int main()
{
    int v = 42; // vstup
    string s = ""; // vystupni text
    int base = 10;
 
    int n = v;
    while (n > 0)
    {
        int d = n % base; // jedna cislice
        char c;
        if (d <= 9)
            c = '0' + d; // jedno pismeno
        else
            c = 'a' + d - 10; // d=10  =>  c='a'
        s = c + s; // pridat na zacatek
        n = n / base; // odstranit nejnizsi cislici
    }
 
    if (v == 0) s = "0"; // pro nulu na vstupu byl vysledkem prazdny retezec
 
    cout << v << " ... " << s << endl;
}