Convert a binary number from type short into a decimal number in C

I need to read from a file a binary number that is represented by type short in C language.

the number represents the size of an array so after I read it I want to use the number as a decimal value.

I tried to convert the binary number into decimal but i get the wrong value.

for example: if the binary numbers in the file are 0000000000000101 , the size in decimal should be 5 but when i use the "classic" binary to decimal i get the value 17.

The "classic" function:

void main()
{
    int  num, binary_val, decimal_val = 0, base = 1, rem;
 
    printf("Enter a binary number(1s and 0s) \n");
    scanf("%d", &num); 
    binary_val = num;
    while (num > 0)
    {
        rem = num % 10;
        decimal_val = decimal_val + rem * base;
        num = num / 10 ;
        base = base * 2;
    }
    printf("The Binary number is = %d \n", binary_val);
    printf("Its decimal equivalent is = %d \n", decimal_val);
}

when i enter just the last 3 numbers (101) i get the value 5 but when i type the full number (0000000000000101) i get 17.

any ideas to solve this? what am I missing here?

thanks

This example works as you wish.

#include <math.h>
#include <stdio.h>
int convert(long long n);
int main() {
    long long n;
    printf("Enter a binary number: ");
    scanf("%lld", &n);
    printf("%lld in binary = %d in decimal", n, convert(n));
    return 0;
}
int convert(long long n) {
    int dec = 0, i = 0, rem;
    while (n != 0) {
        rem = n % 10;
        n /= 10;
        dec += rem * pow(2, i);
        ++i;
    }
    return dec;
}