Compilare: user.cpp: In function ‘int main()’: user.cpp:14:10: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[n]=NULL; ^ user.cpp:16:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(s);i++){ ^ user.cpp:8:54: warning: unused variable ‘j’ [-Wunused-variable] int n=0,k=0,i,top=-1,k2=0,a[5000],k3,b[5000],max=0,j; ^