Main.c: In function 'main': Main.c:6:11: warning: implicit declaration of function 'max' [-Wimplicit-function-declaration] int x=max(n,m); ^ Main.c:5:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&n,&m); ^ /tmp/ccxTClZ7.o: In function `main': Main.c:(.text.startup+0x30): undefined reference to `max' collect2: error: ld returned 1 exit status