View Compilation Error

0_0_15320505_14368.cpp: In function 'int main()':
0_0_15320505_14368.cpp:7:26: error: 'x1' was not declared in this scope
  while(scanf("%f%f%f%f",&x1,&x2,&y1,&y2)!=EOF)
                          ^
0_0_15320505_14368.cpp:7:30: error: 'x2' was not declared in this scope
  while(scanf("%f%f%f%f",&x1,&x2,&y1,&y2)!=EOF)
                              ^
0_0_15320505_14368.cpp:7:34: error: 'y1' was not declared in this scope
  while(scanf("%f%f%f%f",&x1,&x2,&y1,&y2)!=EOF)
                                  ^
0_0_15320505_14368.cpp:7:38: error: 'y2' was not declared in this scope
  while(scanf("%f%f%f%f",&x1,&x2,&y1,&y2)!=EOF)
                                      ^