Compilare: user.cpp: In function ‘int main()’: user.cpp:24:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();i++) ^ user.cpp:11:24: warning: ‘x’ may be used uninitialized in this function [-Wmaybe-uninitialized] int i,j,xx,nr,ok,n,x,l,p,nrr; ^ user.cpp:52:25: warning: ‘op’ may be used uninitialized in this function [-Wmaybe-uninitialized] if(op=='+') ^