/in/foo.c:1:1: error: unknown type name 'def'
 def bianchang(a,b):
 ^~~
/in/foo.c: In function 'bianchang':
/in/foo.c:1:19: error: expected declaration specifiers before ':' token
 def bianchang(a,b):
                   ^
/in/foo.c:1:5: warning: type of 'a' defaults to 'int' [-Wimplicit-int]
 def bianchang(a,b):
     ^~~~~~~~~
/in/foo.c:1:5: warning: type of 'b' defaults to 'int' [-Wimplicit-int]
/in/foo.c:7:1: warning: control reaches end of non-void function [-Wreturn-type]
 print(int(m*n)bianchang(m,n)))
 ^~~~~