foo.cpp: In function 'int main()':
foo.cpp:15:24: error: 'atoi' was not declared in this scope
  start = atoi(l.c_str());
                        ^
foo.cpp:35:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (i = 0;i <= t.length() - 1;i++)
                ^