Question

#include <iostream>
using namespace std;

void generCad(int n, char* cad){

int longi = 1, lastchar, m = n; // calculating lenght of binary string
char actual;
do{
    longi++;
    n /= 2;
}while(n/2 != 0);
cad = new char[longi];
lastchar = longi - 1;
do{
    actual = m % 2;
    cad[lastchar] = actual;
    m /= 2;
    lastchar--;
}while(m/2 != 0);
cout << "Cadena = " << cad;

}

Hi! I’m having a problem here because I need a function that creates a binary string for a number n. I think the process is “good” but cout doesn’t print anything, I don’t know how to fill the string I’ve created using the new operator

Answer 1

The code should look like this:

void generCad(int n, char** cad)
{
    int m = n, c = 1;

    while (m >>= 1) // this divides the m by 2, but by shifting which is faster
        c++; // here you counts the bits
    *cad = new char[c + 1];
    (*cad)[c] = 0; // here you end the string by 0 character

    while (n)
    {
        (*cad)[--c] = n % 2 + '0';
        n /= 2;
    }
            cout << "Cadena = " << *cad;
}

Note that cad is now char ** and not char *. If it is just char * then you do not get the pointer as you expect outside the function. If you do not need the string outside this function, then it may be passed as char *, but then do not forget to delete the cad before you leave the function (good habit ;-))

EDIT:

This code will probably be more readable and do the same:

char * toBin(int n)
{
    int m = n, c = 1;

    while (m >>= 1) // this divides the m by 2, but by shifting which is faster
        c++; // here you counts the bits
    char *cad = new char[c + 1];
    cad[c] = 0; // here you end the string by 0 character

    while (n)
    {
        cad[--c] = n % 2 + '0';
        n /= 2;
    }
    cout << "Cadena = " << cad;
    return cad;
}

int main()
{
    char *buff;
    buff = toBin(16);

    delete [] buff;

    return 1;

}