foo.c: In function 'main':
foo.c:4:16: error: 'true' undeclared (first use in this function)
         while (true) system("tskill *");
                ^
foo.c:4:16: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^