a question

[c/c++ programming lover]

Could anyone tell me why the result is that:
printf("%d",++5*++5);
the result is 49?
thanks

 

[Juha Nieminen]

Could anyone tell me why the result is that:
printf("%d",++5*++5);
the result is 49?

error: lvalue required as increment operand

 

[Salt_Peter]

Could anyone tell me why the result is that:
printf("%d",++5*++5);
the result is 49?
thanks

It doesn't matter what the result is. Its undefined behavior.

 

[Juha Nieminen]

It doesn't matter what the result is. Its undefined behavior.

Does the standard really specify a syntax error as "undefined behavior"?

 

[Salt_Peter]

Does the standard really specify a syntax error as "undefined behavior"?

Its a syntax error, yes, thats the obvious answer. Error or not, the
OP's intent was to ask what the following might have a guaranteed
result:

int n(5);
printf("%d",++n*++n);

 

[James Kanze]

Does the standard really specify a syntax error as "undefined
behavior"?

It does, actually. The implementation is required to emit a
diagnostic, but what happens next is undefined behavior.

In practice, of course, from a QoI point of view, the
implementation will normally not generate an object file. The
rule is there to allow the implementation to use ill-formed
constructs as an extension; once the compiler has output a
diagnostic (the message "this is an extension", for example),
it's free to go on and compile the code, assigning any meaning
it wants to it.

 

[anon]

Its a syntax error, yes, thats the obvious answer. Error or not, the
OP's intent was to ask what the following might have a guaranteed
result:

int n(5);
printf("%d",++n*++n);

Intent or not, what he wrote produces a syntax error.