View Compilation Error

0_0_14967532_1814.cpp: In function 'int main()':
0_0_14967532_1814.cpp:10:33: error: 'X1' was not declared in this scope
     while(scanf("%lf%lf%lf%lf",&X1,&Y1,&X2,&Y2)!=EOF)
                                 ^
0_0_14967532_1814.cpp:10:37: error: 'Y1' was not declared in this scope
     while(scanf("%lf%lf%lf%lf",&X1,&Y1,&X2,&Y2)!=EOF)
                                     ^
0_0_14967532_1814.cpp:10:41: error: 'X2' was not declared in this scope
     while(scanf("%lf%lf%lf%lf",&X1,&Y1,&X2,&Y2)!=EOF)
                                         ^
0_0_14967532_1814.cpp:10:45: error: 'Y2' was not declared in this scope
     while(scanf("%lf%lf%lf%lf",&X1,&Y1,&X2,&Y2)!=EOF)
                                             ^