Convert a binary number to a decimal in C

#include< stdio.h>
#include< stdlib.h>
#include< math.h>

unsigned long int puiss(unsigned long int x, int n)
{
if(n == 0)
return 1;
if(n == 1)
return x;
unsigned long int x2 = powers(x,n/2);
if(n%2 == 0)
return x2*x2;
return x2 * x2 * x;
}
int char_to_int(char d)
{
char str[2];
str[0] = d;
str[1] = '\0';
return (int) strtol(str, NULL, 10);
}

unsigned int convertirEnBase10(int binary)
{
char snum[20];
// convert to String
itoa(binary,snum,10);
// how many characters?
int nc = log10((int)binary)+1;
int decimal = 0;
for(int i = nc-1 ; i >= 0; i--)
{
decimal += char_to_int(snum[i]) * puiss( 2, (nc-1)-i);
}
return decimal;
}

int main()
{
binary int;
while(true)
{
printf("Enter a binary number ");
scanf("%d",& binary);
printf ("%ld in base 2 = %ld in base 10\n",binary, convertInBase10 (binary);
}
return 0;
}