// Program 4 - compute H-H distances <= cutoff
molecule    m;
atom        ai, aj;
float       d, cutoff;

cutoff = atof( argv[ 2 ] );
m = getpdb( "gcg10.pdb" );

for( ai in m ){
    if( ai.atomname !~ "H" )continue;
    for( aj in m ){
        if( aj.tatomnum <= ai.tatomnum )continue;
        if( aj.atomname !~ "H" )continue;
        if(( d=distp(ai.pos,aj.pos))<=cutoff){
            printf(
                "%3d %-4s %-4s %3d %-4s %-4s %8.3f\n",
                ai.tresnum, ai.resname, ai.atomname,
                aj.tresnum, aj.resname, aj.atomname,
                d );
        }
    }
}