foo.c: In function 'main':
foo.c:6:16: error: 'a' undeclared (first use in this function)
    6 |  scanf("%d%d",&a,&b);
      |                ^
foo.c:6:16: note: each undeclared identifier is reported only once for each function it appears in
foo.c:6:19: error: 'b' undeclared (first use in this function)
    6 |  scanf("%d%d",&a,&b);
      |                   ^

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