Having trouble compiling a SAW routine

[laminatedevildoll]

I am trying to compile a sample self-avoiding random walk routine, but my compiler doesn't compile and it gives me error messages due to this line.

int ipos[4] = {};

error 86 - Incomplete expression
error 142 - Void type not permitted here
error 192 - An object of type 'void' cannot be assigned to an object of int

Here's the program:

#include <iostream.h>
#include <stdlib.h>
#include <math.h>

void do_walk (int maxstep, int& nstep, double& rsquared, double& weight ){
const int MAXSTEP=30;
int map[ MAXSTEP*2][MAXSTEP*2]={0};

// start point
int completed=0;
weight=1.0;

int x = MAXSTEP;
int y = MAXSTEP;
int npoint = 1;
map[x][y] = npoint;
do {
int xnew=x;
int ynew=y;

// Check which sites are available
int ipos[4] = {};
int npos = 0;

if( map[x-1][y] == 0 ) {
ipos[npos]=0;
npos++;
}
if( map[x+1][y] == 0 ) {
ipos[npos]=1;
npos++;
}
if( map[x][y-1] == 0 ) {
ipos[npos]=2;
npos++;
}
if( map[x][y+1] == 0 ) {
ipos[npos]=3;
npos++;
}
if( npos == 0 ){
completed =1;
} else {

if( npoint > 1) weight *= npos/3.0;
int i = (int)(npos *(double)rand()/(RAND_MAX+1.0));
switch ( ipos ) {
case 0: xnew-= 1; break;
case 1: xnew+= 1; break;
case 2: ynew-= 1; break;
case 3: ynew+= 1; break;
}

npoint++;
map[xnew][ynew] = npoint;
x = xnew;
y = ynew;
if ( npoint == maxstep+1 )completed=1;
}

} while ( !completed );
//
// Print a window around the centre of the array
//
for ( int i=12; i<2*MAXSTEP-12; i++ ){
for ( int j=12; j < 2*MAXSTEP-12; j++ ){
cout.width(3);
cout << map[j];
}
cout << endl;
}
nstep = npoint-1;
rsquared = pow( x-MAXSTEP,2.0) + pow( y-MAXSTEP, 2.0 );
}

int main(){
int maxstep=50,nstep;
double rsquared,weight;
srand(7654321);
for (int i=1; i<10; i++ ){
do_walk(maxstep,nstep,rsquared,weight);
cout << endl << "Nsteps: " <<nstep << " Rsquared: " <<rsquared<<" Weight: " << weight << endl;
}
return 0;
}

Any help is appreciated. Thank you.

 

[nsimmons]

change
int ipos[4] = {};
to
int ipos[4];

i don't see why the array needs to be zero'd out, if that's what your attempting

 

[ravenprp]

It looks like the issue is with the line "int ipos[4] = {};". In C++, an array must have a size specified within the square brackets, so the correct syntax would be "int ipos[4] = {0};". Additionally, the line "weight *= npos/3.0;" may also cause an error, as the division is between an integer and a double. To fix this, you can change it to "weight *= (double)npos/3.0;". Finally, make sure to include the "using namespace std;" line at the top of your program to avoid having to use "std::" before every standard library function.

I hope this helps. If you continue to have trouble compiling, please provide the specific error messages and we can work through them together. Also, make sure to check for any typos or missing semicolons in your code. Good luck!