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#include <iostream> using namespace std; int main() { int k=5; int m; m=(m=5)+(++k+k++ + ++k+k++); cout<<m<<" "<<k; return 0; }

The compiler gives the out put at 34 and 9 but when i do it manually, I get 33 and 9.

28th Feb 2017, 6:06 AM
Aneesh Satheesh
Aneesh Satheesh - avatar
9 ответов
+ 2
@Aneesh C++ doesn't follow certain definite rules while evaluating multiple prefix and postfix in a single expression. If you would try 10 different compilers you would get 3-4 different results. So multiple prefix and postfix evaluation depends on compiler. But the output for cout<<++a<<a++<<a; would be constant in most compilers.
28th Feb 2017, 8:09 AM
Megatron
Megatron - avatar
+ 1
@Megatron Yeah, true but this was an exam question and i gave the output as 33 and 9 and i got marked wrong for that. So thats why i wanted to know. @Pranav What're you doing here huh xD?
28th Feb 2017, 8:13 AM
Aneesh Satheesh
Aneesh Satheesh - avatar
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I'm getting 26 and 7 on my machine. You sure that's the correct code?
28th Feb 2017, 7:07 AM
DaemonThread
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0
Oh, sorry the 33 and 9 is when k=5!
28th Feb 2017, 7:09 AM
Aneesh Satheesh
Aneesh Satheesh - avatar
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This is actually really strange, but I've done some testing. Check out this code, it might shed some light on this. int main(){ int x = 3; cout << x++ << " " << x++ << endl; return 0; } I get the numbers 4 and 3, in that order. I'm thinking it's because when the numbers are incremented, it happens from right to left. So when you write (m=5)+(++k + k++ + ++k + k++), you're adding the numbers 5, 7, 8, 7, and 7, respectively, which add up to 34.
28th Feb 2017, 7:22 AM
DaemonThread
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After incrementing from right to left we get m=(5)+(9+7+7+5) Which is 33
28th Feb 2017, 7:41 AM
Aneesh Satheesh
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Remember that the prefix increment happens before the rest, so k is incremented to 7 before anything else inside the statement is done. Then it evaluates the postfix increments from right to left, after everything else. So it's closer to (5)+(7+8+7+7), or 34.
28th Feb 2017, 7:54 AM
DaemonThread
DaemonThread - avatar
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I didnt get you, could you explain in steps please
28th Feb 2017, 8:07 AM
Aneesh Satheesh
Aneesh Satheesh - avatar
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But post increment operators have higher precedence right? @Sean
28th Feb 2017, 8:09 AM
Pranav Kumar