在枚举中定义转义，使用enum来控制循环

#include <stdio.h>
enum escapes { BELL = '\a', BACKSPACE = '\b', TAB = '\t',
               NEWliNE = '\n', VTAB = '\v', RETURN = '\r' };

enum months { JAN = 1, FEB, MAR, APR, MAY, JUN,
              Jul, AUG, SEP, OCT, NOV, DEC };
                    /* FEB is 2, MAR is 3, etc. */


int main() {
    printf("BELL, BACKSPACE, TAB, NEWliNE, VTAB, RETURN\n");

    printf("%o %o %o %o %o %o\n",BELL, BACKSPACE, TAB, NEWliNE, VTAB, RETURN);

    for (int i = JAN; i <= DEC; i++)
        printf("%d ", i);

    printf("\n");

    return 0;
}