char s[]="ABCDEFGHJKL";
printf("%%%20s%%\n",s);// %%打印输出% %20s打印输出20长度字符宽度不够补0，默认往右对齐。
printf("%%%-20s%%\n",s); // %-20s打印输出20长度字符宽度不够补空格，-表示往左对齐。
printf("%%%+20s%%\n",s); // %+20s打印输出20长度字符宽度不够补空格，+表示往右对齐。
printf("%%%020s%%\n",s);// %020s打印输出20长度字符宽度不够补0，020表示宽度20不够补0。 
printf("%%%-020s%%\n",s);