C++ 三元运算符c ++中的返回语句
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return statement in ternary operator c++
提问by ameen
I wrote the absolute function using ternary operator as follows
我使用三元运算符编写了绝对函数，如下所示
int abs(int a) {
a >=0 ? return a : return -a;
}
I get the following error messages
我收到以下错误消息
../src/templates.cpp: In function ‘int abs(int)':
../src/templates.cpp:4: error: expected primary-expression before ‘return'
../src/templates.cpp:4: error: expected ‘:' before ‘return'
../src/templates.cpp:4: error: expected primary-expression before ‘return'
../src/templates.cpp:4: error: expected ‘;' before ‘return'
../src/templates.cpp:4: error: expected primary-expression before ‘:' token
../src/templates.cpp:4: error: expected ‘;' before ‘:' token
../src/templates.cpp:5: warning: no return statement in function returning non-void
If I write like this
如果我这样写
return a>=0 ? a : -a;
I don't get any error. What's the difference between the two?
我没有收到任何错误。两者有什么区别？
回答by The Archetypal Paul
The second and third arguments to the ternary operator are expressions, not statements.
三元运算符的第二个和第三个参数是表达式，而不是语句。
return a
is a statement
是一个声明
回答by Nandit Tiku
Your syntax is incorrect. It should be
你的语法不正确。它应该是
if (a >=0)
return a;
else
return -a;
or the way you wanted it:
或者你想要的方式：
return a >=0 ? a : -a;
回答by Gary Willoughby
What's the difference between the two?
两者有什么区别？
One is correct syntax, the other is not.
一种是正确的语法，另一种则不是。
回答by sth
?:is an operator that takes three expressions and evaluates them in some way to produce a result. return ais not an expression(it's a statement), so your first form doesn't work. It's the same as you can't put returnin the arguments of other operators: return a + return bwill also not work.
?:是一个运算符，它采用三个表达式并以某种方式计算它们以产生结果。return a不是表达式（它是语句），因此您的第一种形式不起作用。这与您不能放入return其他运算符的参数相同：return a + return b也将不起作用。
If you want the returns in the separate branches, use ifinstead:
如果您希望在单独的分支中返回，请if改用：
if (a >=0)
return a;
else
return -a;
回答by Jonathan Leffler
Return is a statement and cannot be used where a value is expected.
Return 是一个语句，不能用于需要值的地方。
You must use expressions (which usually yield a value) in the three components of the ternary operator.
您必须在三元运算符的三个组件中使用表达式（通常会产生一个值）。
![C++ new char[10] 和 new char(10) 有什么区别](/res/img/loading.gif)