/in/foo.c: In function 'main':
/in/foo.c:18:5: warning: implicit declaration of function 'fgets' [-Wimplicit-function-declaration]
     fgets(s1);
     ^~~~~
/in/foo.c:24:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
     printf("%d %d", count1, count2);
     ^~~~~~
/in/foo.c:24:5: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:24:5: note: include '<stdio.h>' or provide a declaration of 'printf'