Hi everyone, I am writing an 8-puzzle Problem Solving Program that utilizes the A* (A Star) search algorithm.

I've come this far in completing the desired program, and somehow summed up to this: (entire source code posted below).

But I can't compile it just yet due to this builder error: "**undefined reference to `a_star()'**"

I use Windows XP as my OS, Code Blocks as my IDE. I could provide more of my system specifications if it had to do anything with the error.

I usually get this same type of error with every other projects I make. Everything seemed written right, and yet...

Can anyone help me out with this? Any criticisms, advices, and handy solutions are most welcome and looked forward to. Thanks.

```
#include <iostream>
using namespace std;
int i[9];
int temp[9];
int g[9] = {1,8,7,2,0,6,3,4,5};
int direction[5];
int position;
void input();
void print();
void direct(int k);
int chk(int k);
void copy();
void copyt();
int min(int a,int b,int c,int d);
void up(int k);
void down(int k);
void left(int k);
void right(int k);
void breadth_first();
void depth_first();
int a_star();
void input()
{
int k;
cout << "Input 9 numbers (0,1.....8) following this position:" << endl;
cout << "i0 i3 i6" << endl;
cout << "i1 i4 i7" << endl;
cout << "i2 i5 i8" << endl << endl;
cout << "i0....i8:";
cin >> i[0] >> i[1] >> i[2] >> i[3] >> i[4] >> i[5] >> i[6] >> i[7] >> i[8];
cout << endl;
for(k = 0; k < 9; k++)
{
if(i[k] == 0)
position = k;
}
}
void print()
{
cout << i[0] << " " << i[3] << " " << i[6] << endl;
cout << i[1] << " " << i[4] << " " << i[7] << endl;
cout << i[2] << " " << i[5] << " " << i[8] << endl << endl;
}
void direct(int k)
{
k = position;
if(k == 0 || k == 3 || k == 6)
direction[0] = 0;
else
direction[0] = 1;
if( k == 2 || k == 5 || k == 8)
direction[1] = 0;
else
direction[1] = 1;
if(k == 0 || k == 1 || k == 2)
direction[2] = 0;
else
direction[2] = 1;
if(k == 6 || k == 7 || k == 8)
direction[3] = 0;
else
direction[3] = 1;
}
int chk(int k)
{
int counter = 0;
for(k = 0; k < 9; k++)
{
if(temp[k] != g[k])
counter++;
}
return counter;
}
void copy()
{
int k;
for(k = 0; k < 9; k++)
temp[k] = i[k];
}
void copyt()
{
int k;
for(k = 0; k < 9; k++)
i[k] = temp[k];
}
int min(int a, int b, int c, int d)
{
if(a < b)
{
if(a < c)
{
if(a < d)
return 0;
else
return 3;
}
else
{
if(c < d)
return 2;
else
return 3;
}
}
else
{
if(b < c)
{
if(b < d)
return 1;
else
return 3;
}
else
{
if(c < d)
return 2;
else
return 3;
}
}
}
void up(int k)
{
int temp;
temp = i[k];
i[k] = i[k - 1];
i[k-1] = temp;
}
void down(int k)
{
int temp;
temp = i[k];
i[k] = i[k + 1];
i[k+1] = temp;
}
void left(int k)
{
int temp;
temp = i[k];
i[k] = i[k - 3];
i[k-3] = temp;
}
void right(int k)
{
int temp;
temp = i[k];
i[k] = i[k + 3];
i[k+3] = temp;
}
void breadth_first()
{
}
void depth_first()
{
}
int a_start()
{
int k,u,d,l,r;
u = 99;
d = 99;
l = 99;
r = 99;
k = position;
if(chk(k) == 0)
{
cout << "The puzzle is sorted." <<endl;
return 0;
}
direct(k);
if(direction[0] == 1)
{
copy();
up(k);
u = chk(k);
}
if(direction[1] == 1)
{
copy();
down(k);
d = chk(k);
}
if(direction[2] == 1)
{
copy();
left(k);
l = chk(k);
}
if(direction[3] == 1)
{
copy();
right(k);
r = chk(k);
}
switch (min(u,d,l,r))
{
case 0:
copy();
up(k);
cout << "u ";
position--;
copyt();
a_star();
case 1:
copy();
down(k);
cout << "d ";
position++;
copyt();
a_star();
case 2:
copy();
left(k);
cout << "l ";
position = position - 3;
copyt();
a_start();
case 3:
copy();
right(k);
cout << "r ";
position = position + 3;
copyt();
a_start();
}
return 0;
}
int main()
{
input();
print();
cout << "Movement: ";
a_star();
return 0;
}
```