In the following code:
int c;
while((c=10)>0)
What does c = 10 evaluate to? Is it 1 which indicates that the value 10 is assigned to variable c successfully, or is it 10? Why?
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5 Answers
c = 10 is an expression returning 10 which also assigns 10 to c.
4 Comments
user2131316
if it assigns 10 to c, but should c = 10 return 1?
Bathsheba
That would not be nice, think about the statement a = c = 10; Wouldn't you want a to be 10, not 1?
ramazan polat
It doesn't return 10, it returns
c which is 10 for the first call. The difference is that the value of c will most likely change in the while block.It is said in C99 6.5.16
An assignment operator stores a value in the object designated by the left operand. An
assignment expression has the value of the left operand after the assignment, but is not an
lvalue.
4 Comments
martinkunev
Best answer - clear, precise and short
Max Barraclough
To follow up @martinkunev's answer: this answer is also better because it references the standard directly, and more directly speaks to the question of the type of the expression's value, which matches the type of the left-hand operand. (Consider a=b=c where a and c are unsigned int and b is unsigned short.)
Qix - MONICA WAS MISTREATED
This also means that
int x = 10; int y = (x += 1); results in x = 11, y = 11, not x = 11, y = 1.
Rainald62
Footnote to 6.5.16: "111) The implementation is permitted to read the object to determine the value but is not required to, even when the object has volatile-qualified type." Thus, the value of
gioReg->DSET = 1 << 5 may be 32 (without readback) or larger, if DSET has implicit |= semantics and the compiler happens to generate a read from DSET.Assignment returns with the assigned value. In case c=10 is 10. Since 10!=0, in c it means also true so this is an infinite loop.
It is like you would write
while(10)
Plus You've made the assignment.
If You follow this logic, You can see, that
while(c=0)
would be a loop that never executes its statement or block.
Comments
while((c=10)>0)
c = 10 should return 10.
Now, for while(10>0) 10>0, the > operator returns 1 (non-zero value).
Comments
This is an infinite loop. It first assign 10 to c, then compare it with c > 0, then again loop starts, assign 10 to c, compare it with c>0 and so on. Loop never ends. This is equivalent to the following:
while(c=10);
/* Because c assign a garbage value, but not true for all cases maybe it assign 0 */
while(c);
Edit: It will not return 10 because compiler return only true or false value, so it return true or 1 instead of 10.
5 Comments
Suvarna Pattayil
Why will c be assigned a garbage value?
Ashish Rawat
cause it's not initialized yet and compiler automatically assign some value to this. As all addresses in memory have some value before it initialized
Suvarna Pattayil
c = 10 will it not assign the value 10 to c?Ashish Rawat
It assign 10 to c in 1st statement not in second
Suvarna Pattayil
Oh, I thought its one single block