Integer as an condition in C++'s “ :?” operator
So , for my exam I have to evaluate some C++ expressions.
Here s the expression :
float x=3<<2>>1?4.:.5?6:7>8;
Can someone explain it with words because I can t understand it.
So , I have to convert 3 to binary and shift it 2 bits. But After conversion the result is 11. I may add the bit sign so it becomes 011. And after the bit sign I can add as many 0's as i need and so 3<<2-> 01100. But after that I can't understand a thing.. Where s the condition on the conditional operator ?: because I can't see any?
Thank you in advice for helping me solve this out :)
c++
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
add a comment |
So , for my exam I have to evaluate some C++ expressions.
Here s the expression :
float x=3<<2>>1?4.:.5?6:7>8;
Can someone explain it with words because I can t understand it.
So , I have to convert 3 to binary and shift it 2 bits. But After conversion the result is 11. I may add the bit sign so it becomes 011. And after the bit sign I can add as many 0's as i need and so 3<<2-> 01100. But after that I can't understand a thing.. Where s the condition on the conditional operator ?: because I can't see any?
Thank you in advice for helping me solve this out :)
c++
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
3
Remember that in C++ any non-zero integer value evaluates totrue.
– scohe001
Nov 15 '18 at 22:16
6
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
3
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
1
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14
add a comment |
So , for my exam I have to evaluate some C++ expressions.
Here s the expression :
float x=3<<2>>1?4.:.5?6:7>8;
Can someone explain it with words because I can t understand it.
So , I have to convert 3 to binary and shift it 2 bits. But After conversion the result is 11. I may add the bit sign so it becomes 011. And after the bit sign I can add as many 0's as i need and so 3<<2-> 01100. But after that I can't understand a thing.. Where s the condition on the conditional operator ?: because I can't see any?
Thank you in advice for helping me solve this out :)
c++
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
So , for my exam I have to evaluate some C++ expressions.
Here s the expression :
float x=3<<2>>1?4.:.5?6:7>8;
Can someone explain it with words because I can t understand it.
So , I have to convert 3 to binary and shift it 2 bits. But After conversion the result is 11. I may add the bit sign so it becomes 011. And after the bit sign I can add as many 0's as i need and so 3<<2-> 01100. But after that I can't understand a thing.. Where s the condition on the conditional operator ?: because I can't see any?
Thank you in advice for helping me solve this out :)
c++
c++
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
edited Nov 15 '18 at 22:15
zzxyz
2,2041624
2,2041624
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
asked Nov 15 '18 at 22:13
Andy VavilovAndy Vavilov
183
183
3
Remember that in C++ any non-zero integer value evaluates totrue.
– scohe001
Nov 15 '18 at 22:16
6
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
3
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
1
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14
add a comment |
3
Remember that in C++ any non-zero integer value evaluates totrue.
– scohe001
Nov 15 '18 at 22:16
6
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
3
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
1
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14
3
3
Remember that in C++ any non-zero integer value evaluates to
true.– scohe001
Nov 15 '18 at 22:16
Remember that in C++ any non-zero integer value evaluates to
true.– scohe001
Nov 15 '18 at 22:16
6
6
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
3
3
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
1
1
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14
add a comment |
2 Answers
2
active
oldest
votes
The expression is
3<<2>>1?4.:.5?6:7>8
Let's add some spaces and parens:
((3 << 2) >> 1) ? 4. : (.5 ? 6 : (7 > 8))
Shifting by 1 is just multiplying by 2. Shifting by 2 is multiplying by 2, twice.
So 3 << 2 is 12.
12 >> 1 divides by 2, so that's just 6.
As a condition, all integers (except 0) are true, so this simply returns 4.0.
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
add a comment |
Let's format this a little better:
float x = (3 << 2) >> 1 ? 4. :
.5 ? 6 :
(7 > 8);
Or even better:
float x;
if( 3<<2>>1 ) {
x = 4.;
} else if( .5 ) {
x = 6;
} else {
x = 7 > 8;
}
Walking through the evaluation of 3 << 2 >> 1:
(3 << 2) >> 1 =>
(b0011 << 2) >> 1 =>
b1100 >> 1 =>
b0110 =>
6
Since 6 is a nonzero value (which evaluates to true in C++) x will have the value 4.
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The expression is
3<<2>>1?4.:.5?6:7>8
Let's add some spaces and parens:
((3 << 2) >> 1) ? 4. : (.5 ? 6 : (7 > 8))
Shifting by 1 is just multiplying by 2. Shifting by 2 is multiplying by 2, twice.
So 3 << 2 is 12.
12 >> 1 divides by 2, so that's just 6.
As a condition, all integers (except 0) are true, so this simply returns 4.0.
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
add a comment |
The expression is
3<<2>>1?4.:.5?6:7>8
Let's add some spaces and parens:
((3 << 2) >> 1) ? 4. : (.5 ? 6 : (7 > 8))
Shifting by 1 is just multiplying by 2. Shifting by 2 is multiplying by 2, twice.
So 3 << 2 is 12.
12 >> 1 divides by 2, so that's just 6.
As a condition, all integers (except 0) are true, so this simply returns 4.0.
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
add a comment |
The expression is
3<<2>>1?4.:.5?6:7>8
Let's add some spaces and parens:
((3 << 2) >> 1) ? 4. : (.5 ? 6 : (7 > 8))
Shifting by 1 is just multiplying by 2. Shifting by 2 is multiplying by 2, twice.
So 3 << 2 is 12.
12 >> 1 divides by 2, so that's just 6.
As a condition, all integers (except 0) are true, so this simply returns 4.0.
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
The expression is
3<<2>>1?4.:.5?6:7>8
Let's add some spaces and parens:
((3 << 2) >> 1) ? 4. : (.5 ? 6 : (7 > 8))
Shifting by 1 is just multiplying by 2. Shifting by 2 is multiplying by 2, twice.
So 3 << 2 is 12.
12 >> 1 divides by 2, so that's just 6.
As a condition, all integers (except 0) are true, so this simply returns 4.0.
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
answered Nov 15 '18 at 22:23
melpomenemelpomene
59.9k54693
59.9k54693
add a comment |
add a comment |
Let's format this a little better:
float x = (3 << 2) >> 1 ? 4. :
.5 ? 6 :
(7 > 8);
Or even better:
float x;
if( 3<<2>>1 ) {
x = 4.;
} else if( .5 ) {
x = 6;
} else {
x = 7 > 8;
}
Walking through the evaluation of 3 << 2 >> 1:
(3 << 2) >> 1 =>
(b0011 << 2) >> 1 =>
b1100 >> 1 =>
b0110 =>
6
Since 6 is a nonzero value (which evaluates to true in C++) x will have the value 4.
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
add a comment |
Let's format this a little better:
float x = (3 << 2) >> 1 ? 4. :
.5 ? 6 :
(7 > 8);
Or even better:
float x;
if( 3<<2>>1 ) {
x = 4.;
} else if( .5 ) {
x = 6;
} else {
x = 7 > 8;
}
Walking through the evaluation of 3 << 2 >> 1:
(3 << 2) >> 1 =>
(b0011 << 2) >> 1 =>
b1100 >> 1 =>
b0110 =>
6
Since 6 is a nonzero value (which evaluates to true in C++) x will have the value 4.
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
add a comment |
Let's format this a little better:
float x = (3 << 2) >> 1 ? 4. :
.5 ? 6 :
(7 > 8);
Or even better:
float x;
if( 3<<2>>1 ) {
x = 4.;
} else if( .5 ) {
x = 6;
} else {
x = 7 > 8;
}
Walking through the evaluation of 3 << 2 >> 1:
(3 << 2) >> 1 =>
(b0011 << 2) >> 1 =>
b1100 >> 1 =>
b0110 =>
6
Since 6 is a nonzero value (which evaluates to true in C++) x will have the value 4.
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
Let's format this a little better:
float x = (3 << 2) >> 1 ? 4. :
.5 ? 6 :
(7 > 8);
Or even better:
float x;
if( 3<<2>>1 ) {
x = 4.;
} else if( .5 ) {
x = 6;
} else {
x = 7 > 8;
}
Walking through the evaluation of 3 << 2 >> 1:
(3 << 2) >> 1 =>
(b0011 << 2) >> 1 =>
b1100 >> 1 =>
b0110 =>
6
Since 6 is a nonzero value (which evaluates to true in C++) x will have the value 4.
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
edited Nov 16 '18 at 4:42
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
answered Nov 15 '18 at 22:22
scohe001scohe001
7,87012241
7,87012241
add a comment |
add a comment |
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3
Remember that in C++ any non-zero integer value evaluates to
true.– scohe001
Nov 15 '18 at 22:16
6
This exam question is just silly. Nobody ever writes code like that.
– Paul Sanders
Nov 15 '18 at 22:19
3
Don't worry about understanding it. The code will never pass code review and the dev has been "deleted" ;). I get they want to test on syntax understanding but that example is just laughable.
– NathanOliver
Nov 15 '18 at 22:21
1
Look at the C++ operator precedence table, add parens to group things appropriately. Mind the left-to-right and right-to-left associativity. I would not be surprised if there is a website that will parenthesize the operations of a C++ expression for you.
– Eljay
Nov 15 '18 at 22:22
As a test question it's remarkably ineffective for determining programming knowledge. One can have the grouping order of the shift operations wrong and still get the correct answer.
– doug
Nov 15 '18 at 23:14