CODEWITHSUNDEEP
c++recursionbinarydecimal
DarkSwan
DarkSwan

Reputation: 31

How to write a recursive function that converts a binary numbers into decimal system?

I am trying to write recursive function which converts a binary numbers into decimal system. I couldn't find the bug. Any help will be appreciated deeply.

Here is my first attempt:

#include <iostream>

int sum = 0;
using namespace std;
int powerofO(int taban, int us)
{
    int result = 1;
    for (int i = 1; i <= us; i++)
            result *= taban;
}

int func(int array[], int length, int weight);

int main()
{
    int *size;
    int digits;
    int binary_array[*size];
    cout << "how many digits ? \n";
    cin >> digits;
    *size = digits;
    cout << "Enter your " << digits <<
        " digits binary number using with a space between"
        " each number \n";
    for (int i = 0; i < digits; i++)
            cin >> binary_array[i];
    cout << func(binary_array, digits, -1) << endl;
    return 0;
}

int func(int array[], int length, int weight)
{
    if (length == 0) {
            sum = sum + array[0];
            return sum;
    }
    func(array, length - 1, weight + 1);
    sum = sum + array[length] * powerofO(2, weight);
    return sum;
}

And I tried to rearrange my function to the following, but it is still not working.

int func( int array[],int length ,int weight){
length--;
weight++;
if(length == 0){
sum = sum + array[0] * powerofO(2,weight);
return sum;}   
sum = sum + array[length] * powerofO(2,weight);
func(array,length,weight);}

Upvotes: 2

Views: 3328

Answers (2)

drysdam
drysdam

Reputation: 8637

In func() you are calling func() again before doing the sum. So then when length finally gets to 0, sum only contains the final digit in array[].

Upvotes: 0

sarnold
sarnold

Reputation: 104050

The cause of the immediate segmentation fault is very near the top of the main() function:

int main()
{
    int *size;
    int digits;
    int binary_array[*size];

int *size only declares a pointer to an int, it does not actually allocate memory for that int. *size is used a little later when trying to allocate the array, and the whole thing blows up.

So, a little re-arrangement and the program runs. I don't think the output is correct yet :) but I don't want to take away all your learning opportunities.

#include <iostream>

int sum = 0;
using namespace std;
int powerofO(int taban, int us)
{
    int result = 1;
    for (int i = 1; i <= us; i++)
            result *= taban;
}

int func(int array[], int length, int weight);

int main()
{
    int digits;
    cout << "how many digits ? \n";
    cin >> digits;
    int binary_array[digits];
    cout << "Enter your " << digits <<
        " digits binary number using with a space between"
        " each number \n";
    for (int i = 0; i < digits; i++)
            cin >> binary_array[i];
    cout << func(binary_array, digits, -1) << endl;
    return 0;
}

int func(int array[], int length, int weight)
{
    if (length == 0) {
            sum = sum + array[0];
            return sum;
    }
    func(array, length - 1, weight + 1);
    sum = sum + array[length] * powerofO(2, weight);
    return sum;
}

Upvotes: 2

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