C :

#include <stdio.h>
#include <string.h>
char a[1005][85];
int w, h;
int dfs(int i, int j)
{
	if (i < 1 || j < 1 || i > h || j > w) return 0;
	int cnt = 0;
	if (a[i][j] == '*')
	{
		cnt = 1;
		a[i][j] = '.';
		cnt += dfs(i, j + 1);
		cnt += dfs(i, j - 1);
		cnt += dfs(i + 1, j);
		cnt += dfs(i - 1, j);
	}
	return cnt;
}
int main(int argc, char *argv[])
{
	memset(a, '\0', sizeof(a));
	scanf("%d%d", &w, &h);
	getchar();
	int i, j;
	for (i = 1; i <= h; i++)
	{
		for (j = 1; j <= w; j++)
			scanf("%c", &a[i][j]);
		getchar();
	}
	int t = 0, s = 0;
	for (i = 1; i <= h; i++)
	{
		for (j = 1; j <= w; j++)
		{
			t = dfs(i, j);
			s = s > t ? s : t;
		}
	}
	printf("%d\n", s);
	return 0;
}

C++ :

#include <iostream> 
#include <iomanip> 
#include <cmath> 
#include <string> 
#include <cstring> 
using namespace std; 
int w,h,ph[1002][82],q1[80004],q2[80004],f,r,s,maxs=0; 
char ch; 
int main() 
{ 
    cin>>w>>h; 
    for (int i=1;i<=h;i++)  
        for (int j=1;j<=w;j++) {cin>>ch; if (ch=='*'){ph[i][j]=1;}}  
          
     for (int i=1;i<=h;i++)  
        for (int j=1;j<=w;j++) 
        { 
         if (ph[i][j]==1) 
         { 
            r=1; q1[r]=i; q2[r]=j; f=0; s=0; 
            while (f<=r) 
            { 
              f++; s++; 
              ph[q1[f]][q2[f]]=0; 
              if (ph[q1[f]-1][q2[f]]==1) 
               {r++; q1[r]=q1[f]-1; q2[r]=q2[f]; ph[q1[f]-1][q2[f]]=0;} 
              if (ph[q1[f]][q2[f]-1]==1)  
               {r++; q1[r]=q1[f]; q2[r]=q2[f]-1; ph[q1[f]][q2[f]-1]=0;} 
              if (ph[q1[f]][q2[f]+1]==1)  
               {r++; q1[r]=q1[f]; q2[r]=q2[f]+1; ph[q1[f]][q2[f]+1]=0;} 
              if (ph[q1[f]+1][q2[f]]==1) 
               {r++; q1[r]=q1[f]+1; q2[r]=q2[f]; ph[q1[f]+1][q2[f]]=0;} 
            } 
//            for (int i=1;i<=20;i++)  cout<<setw(3)<<q1[i];cout<<endl; 
//            for (int i=1;i<=20;i++)  cout<<setw(3)<<q2[i];cout<<endl; 
            if (s>maxs) maxs=s; 
         }    
        } 
        if (maxs>0) maxs--; 
    cout<<maxs<<endl; 
//    system ("pause"); 
    return 0; 
}