escape sequence "c"

#include <stdio.h>
int main()
{
    printf("Hello World !c");
    return 0;
}

[10:40:36@wjshan0808 ~/Documents/C Program]$ gcc printf.c
printf.c:4:9: warning: unknown escape sequence 'c'
[10:41:52@wjshan0808 ~/Documents/C Program]$ g++ printf.c
printf.c: In function ‘int main()’:
printf.c:4: warning: unknown escape sequence 'c'
[10:42:20@wjshan0808 ~/Documents/C Program]$ cc printf.c
printf.c:4:9: warning: unknown escape sequence 'c'