i'm puzzled with this statement
Hi friends,
Please tell me why the following statements are legal in C.
(At least, turbo c++ doesn't give an error!).
int x,y;
x = 2,3,4;
y = (2,3,4);
This evaluates to x=2 and y=4.
But why? Shouldn't it give a compilation error?
Please tell me why the following statements are legal in C.
(At least, turbo c++ doesn't give an error!).
int x,y;
x = 2,3,4;
y = (2,3,4);
This evaluates to x=2 and y=4.
But why? Shouldn't it give a compilation error?
It is legal in many languages - the comma operator evaluates each of its arguments and returns the last. It's useful in some cases.
the statement
x = 2,3,4;
is:
x gets 2;
3;
4;
It's effectively the same as x = 2;3;4; which doesn't do anything with 3 and 4.
x = (2,3,4);
is
2;
3;
x gets 4;
Try not to use comma's too often in normal statements. The only times I ever use them are:
1. Parameter lists
2. Multiple definitions
3. for loops:
though some people frown upon usage #3 in this list as it makes things a little harder to read.
x = 2,3,4;
is:
x gets 2;
3;
4;
It's effectively the same as x = 2;3;4; which doesn't do anything with 3 and 4.
x = (2,3,4);
is
2;
3;
x gets 4;
Try not to use comma's too often in normal statements. The only times I ever use them are:
1. Parameter lists
int pow(int a, int b);2. Multiple definitions
int a, b, c;3. for loops:
for (int a = 1, b = 10; a < b; ++a, --b)though some people frown upon usage #3 in this list as it makes things a little harder to read.
Last edited on
Ahh, I found a good reference on WHY:
http://en.cppreference.com/w/cpp/language/operator_precedence
The assignment operator = (15) has a higher precedence than , (17). So:
x = 2,3,4; is
"(x = 2) then 3 then 4"
versus
x = (2,3,4);
"x = (2 then 3 then 4)"
"x = (4)
http://en.cppreference.com/w/cpp/language/operator_precedence
The assignment operator = (15) has a higher precedence than , (17). So:
x = 2,3,4; is
"(x = 2) then 3 then 4"
versus
x = (2,3,4);
"x = (2 then 3 then 4)"
"x = (4)
Last edited on
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