foo.c: In function 'S':
foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
   14 | }
      | ^
foo.c: In function 'X':
foo.c:26:1: warning: control reaches end of non-void function [-Wreturn-type]
   26 | }
      | ^
foo.c: In function 'main':
foo.c:30:11: warning: 'a' is used uninitialized [-Wuninitialized]
   30 |         s=S(a,b);
      |           ^~~~~~
foo.c:29:13: note: 'a' was declared here
   29 |         int a,b,s,x;
      |             ^
foo.c:30:11: warning: 'b' is used uninitialized [-Wuninitialized]
   30 |         s=S(a,b);
      |           ^~~~~~
foo.c:29:15: note: 'b' was declared here
   29 |         int a,b,s,x;
      |               ^

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