/in/foo.c: In function 'main':
/in/foo.c:6:2: error: 'c' undeclared (first use in this function)
  c=a+b;
  ^
/in/foo.c:6:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:10: warning: format '%d' expects argument of type 'int *', but argument 2 has type 'long long int *' [-Wformat=]
  scanf("%d %d",&a,&b);
          ^
/in/foo.c:7:13: warning: format '%d' expects argument of type 'int *', but argument 3 has type 'long long int *' [-Wformat=]
  scanf("%d %d",&a,&b);
             ^