/in/foo.c: In function 'main':
/in/foo.c:9:2: warning: implicit declaration of function 'itoa' [-Wimplicit-function-declaration]
  itoa(x,str,2);
  ^~~~
/tmp/ccDUrWR6.o: In function `main':
foo.c:(.text.startup+0x29): undefined reference to `itoa'
collect2: error: ld returned 1 exit status