Error linking standard header file in gcc

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http://askubuntu.com – I've a simple code: #include <stdio.h> #include <stdlib.h> int main() { int x=99; char str[100]; itoa(99, str, 10); return 0; } Trying to compile in using terminal in gcc with : gcc test.c But I get the error: /tmp/ccJN77g6.o: In function `main': test.c:(.text+0x35): undefined reference to `itoa' collect2: ld returned 1 exit status Why so? prototype for itoa is included in stdlib.h (HowTos)