View Compilation Error

0_0_24039580_21411.cpp: In function 'double tr_area(point, point, point)':
0_0_24039580_21411.cpp:28:17: error: expected identifier before '(' token
     return 0.5*[(a.x*b.y-b.x*a.y)+(b.x*c.y-c.x*b.y)+(c.x*a.y-a.x*c.y)];
                 ^
0_0_24039580_21411.cpp: In lambda function:
0_0_24039580_21411.cpp:28:71: error: expected '{' before ';' token
     return 0.5*[(a.x*b.y-b.x*a.y)+(b.x*c.y-c.x*b.y)+(c.x*a.y-a.x*c.y)];
                                                                       ^
0_0_24039580_21411.cpp: In function 'double tr_area(point, point, point)':
0_0_24039580_21411.cpp:28:15: error: no match for 'operator*' (operand types are 'double' and 'tr_area(point, point, point)::<lambda()>')
     return 0.5*[(a.x*b.y-b.x*a.y)+(b.x*c.y-c.x*b.y)+(c.x*a.y-a.x*c.y)];
               ^
0_0_24039580_21411.cpp: In function 'int main()':
0_0_24039580_21411.cpp:41:18: error: 'start' was not declared in this scope
    area+=tr_area(start,last,cur);
                  ^