foo.c:3:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main()
 ^~~~
foo.c: In function 'main':
foo.c:12:8: warning: unused variable 'j' [-Wunused-variable]
  int i,j;
        ^
foo.c:15:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:16:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%ld",&num);
  ^~~~~~~~~~~~~~~~~
foo.c:18:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&x[i],&y[i]);
     ^~~~~~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。