foo.c: In function 'main':
foo.c:8:30: warning: unused variable 'result' [-Wunused-variable]
  int a1[100],a2[100],a3[100],result[200],len1,len2,len3,i;
                              ^~~~~~
foo.c:9:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d",&len1,&len2,&len3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:12:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a1[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:16:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a2[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:20:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a3[i]);
   ^~~~~~~~~~~~~~~~~~