whitequark@raidho:~$ cat >test.c
int main() {
  float a = 12.345678;
  printf("%.4f\n", a);
}
whitequark@raidho:~$ gcc test.c -o test
test.c: In function ‘main’:
test.c:3:3: warning: incompatible implicit declaration of built-in function ‘printf’ [enabled by default]
whitequark@raidho:~$ ./test
12.3457