/in/foo.c: In function 'main':
/in/foo.c:18:8: error: 'a' undeclared (first use in this function)
     if(a[i] == (a[j] + a[k]) && i != k && i != j && j != k)
        ^
/in/foo.c:18:8: note: each undeclared identifier is reported only once for each function it appears in