Compilare: user.cpp: In function ‘void sortinfold()’: user.cpp:23:65: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] for(q=0,w=l;a[w]>='0';++q,++w){c[t].a[q]=a[w];}c[t].a[q]=NULL; ^ user.cpp:39:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k=c[l].b;k<=c[l].e;++k,++h){a[h]=d[k];} ^ user.cpp: In function ‘int main()’: user.cpp:64:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[j]=NULL; ^ user.cpp:67:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[j]=NULL; ^ user.cpp:73:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[j]=NULL; ^