View Compilation Error

0_0_28523116_31500.c: In function 'main':
0_0_28523116_31500.c:6:12: error: called object is not a function or function pointer
          l=(a+c)(a-c)+(b+d)(b-d);
            ^
0_0_28523116_31500.c:6:23: error: called object is not a function or function pointer
          l=(a+c)(a-c)+(b+d)(b-d);
                       ^