int main(void){
    int a[]={0, 0, 0, 0, 0, 0, 0};
    int n = 7,
        i,
        index = 0;
 
   while(index < n && a[index]) index++; // skip initial 1's
   for(i = index; i < n; i++){  
     if(a[i]) a[index++] = 1;    
     a[i] = 0;
   }
 
   for(i = 0; i < n; i++){
        printf("%3d", a[i]);
   }
    return 1;
}