def cross_product(v1, v2)
    : return v1[0] * v2[1] -
    v1[1] * v2[0]

        def is_convex_quadrilateral(A, B, C, D)
    : AB = (B[0] - A[0], B[1] - A[1]) BC = (C[0] - B[0], C[1] - B[1]) CD = (D[0] - C[0], D[1] - C[1]) DA =
    (A[0] - D[0], A[1] - D[1])

        cross_AB_BC = cross_product(AB, BC) cross_BC_CD = cross_product(BC, CD) cross_CD_DA =
            cross_product(CD, DA) cross_DA_AB =
                cross_product(DA, AB)

#检查所有叉积是否具有相同的符号
                    if (cross_AB_BC > 0 and cross_BC_CD > 0 and cross_CD_DA > 0 and cross_DA_AB > 0) or
                (cross_AB_BC < 0 and cross_BC_CD < 0 and cross_CD_DA < 0 and cross_DA_AB < 0)
    : return True #是凸多边形 else : return False #不是凸多边形

/sandbox/1/a.c:1:1: error: unknown type name 'def'
def cross_product(v1, v2):
^
/sandbox/1/a.c:1:26: error: expected function body after function declarator
def cross_product(v1, v2):
                         ^
/sandbox/1/a.c:15:7: error: invalid preprocessing directive
    # 检查所有叉积是否具有相同的符号
      ^
3 errors generated.