foo.c: In function ‘main’:
foo.c:15:21: warning: implicit declaration of function ‘add1’ [-Wimplicit-function-declaration]
   15 |                 x = add1(t1, t2, a, b);
      |                     ^~~~
foo.c:16:21: warning: implicit declaration of function ‘add2’ [-Wimplicit-function-declaration]
   16 |                 y = add2(t1, t2, a, b);
      |                     ^~~~