Error message: invalid types 'bool...' (array problem)

Applications Programming
1

Hello everyone.

I'm stuck with an error message that neither I nor any of my computer science peeps can understand. The program I wrote is meant to be a simple decimal to binary converter, but with this message it's more complicated than I thought.

Here's the code:

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	int num = 0;
	double k = 0;
	int max = 0;
	bool binary[100];
	cout << "Enter a decimal number: " ; 
		cin >> num;
		
	while (pow(2,k) <= num)
		k++;
		
	k--;				// Decrements the power after the highest power of 2 is found.	  
	max = k;
	
	while (k >= 0 && num > 0)
	{
		if (pow(2,k) > num)
			binary[k] = 0;
		else
		{
			binary[k] = 1;
			num -= pow(2,k);
		}
		k--;
	}
	
	while (max >= 0)
	{
		cout << binary[max];
		max++;
	}
	
return 0;
}

The error exactly says:
...\dectobin.cpp:27: error: invalid types 'bool [100][double]' for array subscript
...\dectobin.cpp:30: error: invalid types 'bool [100][double]' for array subscript

If it helps, I'm using Quincy... but only because my lecturer is using Quincy.

Any help is appreciated greatly.

PS, is there any reason why the variable k can't be of type int?

2

There's no such thing as array[3.14159]. It has to be a whole integer. So floating point numbers as array indexes make no sense.

You could make k an integer, and it'd spew warnings, but it'd work. Using pow() is severe overkill, though -- your numbers are already binary. Just use binary operators to get at the bits in num instead of converting to float, doing exponents, and converting back.

#include <iostream>
#include <cmath>
using namespace std;

int main(void)
{
	unsigned int num, q;
	cout << "Enter a decimal number: " ; 
		cin >> num;

        for(q=31; q >= 0; q--)
        {
                // Shift the number q bits to the right, then check if bit 1 is set.
                if((num >> q) & 1) cout << "1";
                else                     cout << "0";
        }

        return(0);
}
3

Although I would very much like to do this, the binary equivalent has to be stored within an array... =[

Also, I actually did declare k as type int before, but that produced even more problems for me... it said on lines 14, 22 and 27:
error: call of overloaded 'pow(int, int&); is ambiguous
note: candidates are: double pow(double, double)

4

This is suddenly sounding like homework. We have a homework forum and special homework rules to be followed, please use them.

You can easily store in an array instead of printing them while using my method. There's still no reason to use pow().

You might need to typecast things to double to do so. C++ is a little stricter about this than C.