escape sequence "\c"

#include <stdio.h>
int main()
{
    printf("Hello World !\c");
    return ;
}

[::@wjshan0808 ~/Documents/C Program]$ gcc printf.c
printf.c::: warning: unknown escape sequence '\c'
[::@wjshan0808 ~/Documents/C Program]$ g++ printf.c
printf.c: In function ‘int main()’:
printf.c:: warning: unknown escape sequence '\c'
[::@wjshan0808 ~/Documents/C Program]$ cc printf.c
printf.c::: warning: unknown escape sequence '\c'