Convertir un nombre d'une base vers une autre base en C

#include <stdio .h="">
long convertirEnBase10 (long n, int base)
{
 long quotient = n / 10;
 long reste = n % 10;
 if (quotient == 0)
 return reste;
 else
 return convertirEnBase10 (quotient, base) * base + reste;
}
long convertirEnBase2 (long n, int base)
{
 long quotient = n / 2;
 long reste = n % 2;
 if (quotient == 0)
 return reste;
 else
 return convertirEnBase2 (quotient, base) * base + reste;
}

long convertirEnBase4 (long n, int base)
{
 long quotient = n / 4;
 long reste = n % 4;
 if (quotient == 0)
 return reste;
 else
 return convertirEnBase4 (quotient, base) * base + reste;
}

long convertirEnBase8 (long n, int base)
{
 long quotient = n / 8;
 long reste = n % 8;
 if (quotient == 0)
 return reste;
 else
 return convertirEnBase8 (quotient, base) * base + reste;
}

long convertirEnBase16 (long n, int base)
{
 long quotient = n / 16;
 long reste = n % 16;
 if (quotient == 0)
 return reste;
 else
 return convertirEnBase16 (quotient, base) * base + reste;
}

int main () {
 long n = 17;
 int base = 10;
 //Décimal --> base(2,4,8,16)
 printf ("%ld en base %2d = %ld en base 2\n",n, base, convertirEnBase2 (n, base) );
 printf ("%ld en base %2d = %ld en base 4\n",n, base, convertirEnBase4 (n, base) );
 printf ("%ld en base %2d = %ld en base 8\n",n, base, convertirEnBase8 (n, base) );
 printf ("%ld en base %2d = %ld en base 16\n",n, base, convertirEnBase16 (n, base) );
 
 //Binaire --> Décimal
 n = 1010;
 base = 2;
 printf ("%ld en base %2d = %ld en base 10\n",n, base, convertirEnBase10 (n, base) );
 
 //Héxadécimal --> Décimal
 n = 124;
 base = 16;
 printf ("%ld en base %2d = %ld en base 10\n",n, base, convertirEnBase10 (n, base) );
 
 //base 8 --> binaire
 n = 12;
 base = 8;
 printf ("%ld en base %2d = %ld en base 10\n",n, base, convertirEnBase10 (n, base) );
 
 return 0;
}