foo.c: In function 'main':
foo.c:6:27: warning: unused variable 'flag' [-Wunused-variable]
  int i,n,w,a[100],j,num=0,flag=0;
                           ^~~~
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&w);
  ^~~~~~~~~~~~~~
foo.c:8:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ^~~~~~~~~~~~~~
foo.c:11:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);//a[i]里是价格
   ^~~~~~~~~~~~~~~~~