Unresolved Externals?

[NZheadshot]

So I've written out a program that is supposed to convert hexadecimal numbers to normal numerals. however, i keep getting this error:

Error 6 error LNK2019: unresolved external symbol "double __cdecl cNum(char * const,int)" (?cNum@@YANQADH@Z) referenced in function _main c:\Users\Username\documents\visual studio 2012\Projects\HexAdder\Source.obj HexAdder

Anyone know what this means???

Here's my code for reference:

#include <iostream>
#include <cmath>
using namespace std;
void fill_array(char a[], int size);
double cNum(char a[], int size);
const int SIZE = 10;
int main()
{
	char hex1[SIZE], hex2[SIZE];
	int number_used;
	double num1, num2;
	num1 = cNum(hex1, SIZE);
	fill_array(hex1, SIZE);
	for (int i = 0; i <= (SIZE - 1); i++)
		cout << hex1[i];
	cout << endl << num1;
	system("pause");
	return 0;
}
void fill_array(char a[], int size)
{
	cout << "Enter a number in hexadecimal format up to 10 digits long\n"
		<< "Mark the end with an asterisk(*)\n";
	char next;
	int i = (size - 1);
	cin >> next;
	while (i >= 0)
	{
		if (next != '*')
		{
			a[i] = next;
			i--;
			cin >> next;
		}
		else
		{
			a[i] = '0';
			i--;
		}
	}
}
double cNum(const char hex[], const int size)
{
	double sum;
	char a[SIZE];
	for (int i = 0; i < size; i++)
	{
			switch (hex[i])
		{
				case '0':
					a[i] = 1;
				case '1':
					a[i] = 2;
				case '2':
					a[i] = 3;
				case '3':
					a[i] = 4;
				case '4':
					a[i] = 5;
				case '5':
					a[i] = 6;
				case '6':
					a[i] = 7;
				case '7':
					a[i] = 8;
				case '8':
					a[i] = 9;
				case '9':
					a[i] = 10;
				case 'a':
					a[i] = 11;
				case 'b':
					a[i] = 12;
				case 'c':
					a[i] = 13;
				case 'd':
					a[i] = 14;
				case 'e':
					a[i] = 15;
				case 'f':
					a[i] = 16;
		}
			a[i] = pow(16, i) * hex[i];
			sum += a[i];
	}
		return sum;
}

Also, that switch is huge and unruly. Anyone have any other suggestions to converting?

[Volatile Pulse]

Your prototype: double cNum(char a[], int size);

Your definition: double cNum(const char hex[], const int size)

They need to be the same.