foo.cpp: In function 'int main(int, char**)':
foo.cpp:29:19: error: 'system' was not declared in this scope
foo.cpp:16:8: warning: unused variable 'b' [-Wunused-variable]
foo.cpp:16:12: warning: unused variable 'd' [-Wunused-variable]
foo.cpp:16:14: warning: unused variable 'e' [-Wunused-variable]