foo.c: In function 'Merge':
foo.c:27:3: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
   for(k=j+1;k<n1+n2;k++)
   ^~~
foo.c:34:4: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    for(j=0;j<n1+n2;j++)
    ^~~
foo.c: In function 'main':
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n1,&n2,&n3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:9:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a1[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:11:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a2[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:13:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a3[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c: In function 'Merge':
foo.c:36:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^