%d,\n是什么意思，小括号里打上“我今年18岁”不行吗？小括号里面的内容不是很明白
例如：
int age=18;
printf("我今年%d岁\n",age);
其中%d的意思是输出整形变量，\n的意思是输出换行符
输出函数格式一般为printf("[输出变量格式][换行符、制表符]",[已声明的变量])
%d：整形变量
%f：浮点型变量
%lf：双精度型变量
%c：字符型变量（声明字符型变量时用单引号）
%s：字符串型变量
……
换行符（键盘回车键）：\n
制表符（键盘TAB键）：\t
……
小括号中的内容也可以是其他文字，所以printf("我今年18岁")也是合法的
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