There are a lot of differences between C and C++ and came to stuck on one of them The same code gives an error in C while just executes fine in C++ Please explain the reason
int main(void)
{
int a=10,b;
a>=5?b=100:b=200;
}
The above code gives an error in C stating lvalue required while the same code compiles fine in C++
Have a look at the operator precedence.
Without an explicit () your code behaves like
( a >= 5 ? b = 100 : b ) = 200;
The result of a ?: expression is not a modifiable lvalue [#] and hence we cannot assign any values to it.
Also, worthy to mention, as per the c syntax rule,
assignment is never allowed to appear on the right hand side of a conditional operator
Relared Reference : C precedence table.
OTOH, In case of c++, well,
the conditional operator has the same precedence as assignment.
and are grouped right-to-left, essentially making your code behave like
a >= 5 ? (b = 100) : ( b = 200 );
So, your code works fine in case of c++
[ # ] -- As per chapter 6.5.15, footnote (12), C99 standard,
A conditional expression does not yield an lvalue.
Because C and C++ aren't the same language, and you are ignoring the assignment implied by the ternary. I think you wanted
b = a>=5?100:200;
which should work in both C and C++.
In C you can fix it with placing the expression within Parentheses so that while evaluating the assignment becomes valid.
int main(void)
{
int a=10,b;
a>=5?(b=100):(b=200);
}
The error is because you don't care about the operator precedence and order of evaluation.
来源：https://stackoverflow.com/questions/28337054/ternary-operator-in-c-vs-c