/in/foo.c: In function 'main':
/in/foo.c:9:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
     scanf("%d",&n);
     ^~~~~
/in/foo.c:9:5: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:9:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:24:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
     printf("%d\n",find_max(b,n));
     ^~~~~~
/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'
/in/foo.c:24:19: warning: implicit declaration of function 'find_max' [-Wimplicit-function-declaration]
     printf("%d\n",find_max(b,n));
                   ^~~~~~~~