src.c: In function 'hef':
src.c:18:3: error: 't' undeclared (first use in this function)
t = u, u = v, v = t;
^
src.c:18:3: note: each undeclared identifier is reported only once for each function it appears in
src.c:20:10: error: 'r' undeclared (first use in this function)
while ((r = u%v) != 0)
^