Output of C program

Question

int a[]={10,20,30,40};
int x=0;

int v=a[++x]+ ++x + a[--x];
printf("%d",v);

What will be the output of this program??

Completely confused with the output. No way it is going to be done according to my operator precedence knowledge.

According to me, in this expression Array subscripting [] has highest precendence and should be executed first. so both [] should be executed first from left to right. In this case value of x will increment first, then decrement and finally come back to 0. so expression will become int v=a[0] + ++x + a[0]. Then the pre increment is having highest precedence and it will be incremented to 1. so our expression will become int v=a[0]+1+a[0]. so final output will be 21.

But this is not the case. I have checked on different compiler implementations and no one prints 21.

I am much surprised because the value printed is 43, which is no where understandable to me. That's why I want someone to help me understand and come to the result 43.

The link which others have suggested is using only increment and same rvalue and lvalue cases. But this is somewhat different and not clear. I tried to contruct expression tree for this and solve but 43 is no where in scope.

atleast someone should tell me what would be the order of sub expression evaluation. — vicky, May 03 '13 at 09:02

score 2 · Accepted Answer · answered May 02 '13 at 11:07

2

Output of this code:

int v=a[++x]+ ++x + a[--x];

is undefined and it depends on the compiler implementation.

answered May 02 '13 at 11:07

Alex

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yes it depends on compiler implementation. But assuming one particular compiler can't we guess one output which satisfies our logic. – vicky May 03 '13 at 09:01

Output of C program

1 Answers1