View Compilation Error

0_0_22838836_23570.c: In function 'main':
0_0_22838836_23570.c:6:53: error: lvalue required as left operand of assignment
  while(scanf("%lf%lf%lf%lf",a[0],a[0]+1,a[1],a[1]+1)=4)
                                                     ^