foo.cpp:5:7: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main ()
       ^
foo.cpp: In function 'int main()':
foo.cpp:16:4: error: 'tt' was not declared in this scope
 s+=tt;
    ^
foo.cpp:19:4: error: 'nt' was not declared in this scope
 s+=nt;
    ^