/in/foo.cc: In function 'int main()':
/in/foo.cc:9:40: warning: operation on 'j' may be undefined [-Wsequence-point]
   if(x>1){c[j]=1;for(int z=1;z<x;z++)a[++j]=a[j-1],b[j]=b[j-1],c[j]=1;}
                                        ^~~