I am using this statement
if ((pm && pn) || (pm == false && pn == false))
it is supposed to return true only if both pm and pn are true or if both are false. But this is also returning true if only only first one (pm) is true.
So now it is acting like this:
0 0 = 1
0 1 = 0
1 0 = 1
1 1 = 1
but I need it to work like this:
0 0 = 1
0 1 = 0
1 0 = 0
1 1 = 1
can you tell me where am I making mistake?
What you want is simply:
if (pm == pn)
You are checking if pm is true twice. You also need to check if both are the same, not whether they are both true. So,
if ((pm == pn)
^^ ^^
pm && pm
should be
pm && pn
^
The whole expression can be simplified to
pm == pn
if the variables already have bool type.
Why not try xor?
if (!(pm ^ pn)) { /*...*/ }
Or simply equal?
if (pm == pn) { /*...*/ }
if ((pm && pm) || (pm == false && pn == false))
it is supposed to return true only if both pm and pn are true or if both are false. But this is also returning true if only only first one (pm) is true.
Because you made a typo. You meant pm && pn.
Instead just write if (pm == pn), which is equivalent along as the only semantic values are indeed true and false for both variables.
Plus, consider making your variable names clearer and more distinct.
Note that operator precedence has nothing to do with this.
Since the question's title asks about precedence, note that || has lower precedence than &&. So the two sets of inner parentheses are redundant, and the original expression is just a longer way of saying
if (pm && pm || pm == false && pn == false)
Now, fixing the obvious typo:
if (pm && pn || pm == false && pn == false)
Removing the unneeded explicit comparisons:
if (pm && pn || !pm && !pn)
And, finally, a less obvious transformation, which others have suggested:
if (pm == pn)
Related
I have this if statement and it is not working:
if (pEntry->GetStudentMaterialStudyPoint(StudentAssign::kBibleReading) == 1 &&
(pEntry->GetStudentMaterialStudyPoint(StudentAssign::kItem1) == 1 && LOBYTE(LOWORD(pEntry->GetStudentAssignFlags()))) &&
(pEntry->GetStudentMaterialStudyPoint(StudentAssign::kItem2) == 1 && HIBYTE(LOWORD(pEntry->GetStudentAssignFlags()))) &&
(pEntry->GetStudentMaterialStudyPoint(StudentAssign::kItem3) == 1 && LOBYTE(HIWORD(pEntry->GetStudentAssignFlags()))) &&
(pEntry->GetStudentMaterialStudyPoint(StudentAssign::kItem4) == 1 && HIBYTE(HIWORD(pEntry->GetStudentAssignFlags()))))
{
MWBValidationErrorStruct errorMWBValidation;
errorMWBValidation.iDateIndex = iDateIndex;
errorMWBValidation.datMeeting = pEntry->GetMeetingDate();
errorMWBValidation.eValidationErrorType = CChristianLifeMinistryDefines::MWBValidationErrorType::MaterialStudyPoints;
m_listValidationErrors.push_back(errorMWBValidation);
}
}
I am trying to find out if all of the items have a value of 1. The first item (bible reading) will always be checked. But the items 1 to 4 only need to be checked if they are "included". That is what the LOBYTE(LOWORD(pEntry->GetStudentAssignFlags())) is for.
So,
Bible Reading - 1
Item 1 - 1
Item 2 - 1 - Not included
Item 3 - 1 - Not included
Item 4 - 1 - Not included
In the above scenario the if should be true because both BR and Item 1 are set to 1. We ignore the other 3 items.
Bible Reading - 1
Item 1 - 2
Item 2 - 3
Item 3 - 1 - Not included
Item 4 - 1 - Not included
In the above scenario the if should return false because all the values are not 1 and we are ignoring the last two items.
What is wrong with my if logic?
You should use (!included || x == 1) to ignore checking an item if it's not included. Because of short circuiting, if included is false, you won't even check the other side of the OR, which is exactly what you want.
Your if could look like:
if (pEntry->GetStudentMaterialStudyPoint(StudentAssign::kBibleReading) == 1 &&
(!LOBYTE(LOWORD(pEntry->GetStudentAssignFlags())) || pEntry->GetStudentMaterialStudyPoint(StudentAssign::kItem1) == 1) &&
...
This may be a little confusing, so let's make a truth table...
included | x | !included | x == 1 | (!included || x == 1)
------------------------------------------------------
false | 3 | true | false | true
true | 3 | false | false | false
true | 1 | false | true | true
If included = false, then !included will be true, so (!included || x == 1) will always be true. This is what we want--if we're not included, just evaluate to true without even checking x == 1.
If included = true, then !included is false, so the value of (!included || x == 1) will be whatever x == 1 is. Which is again what we want. If we're included, then depend on x == 1.
This is very simple question, but I can't get it. I have simple condition:
bool c = true || true || true && false;
Why this evaluation is true? As far as I know it evaluates like this:
true || true || true && false => true || true && false => true && false => false
But guess im wrong.
You just have to learn some few basic rules:
(a OR b) is true IF AND ONLY IF at least one of a or b is true.
(a AND b) is true IF AND ONLY IF both of a and b are true.
ORDER of Operators MATTERS: you can't just do the logic any way that you want. computer calculates the output of the a logical statement by an order. a simplified order is like this: First is Grouping (), Second is And, Third is OR.
so when you say bool c = true || true || true && false;. the computer says ok let's first calculate true && false. it is false! and then it calculates true || true || false which is true.
EDIT
Note 1: a complete list of logical operators and their precedence is heavily dependent on the language. you can refer to the documentation for that.
for C#
Note 2: the best practice is to use GROUPING like parenthesis because GROUPING is always of priority. for example it's better to say:
bool c = (true || true) || (true && false);
Think of OR || like addition and AND && as multiplication. There is a priority in there, in fact, you will sometimes see them written as such:
bool c = true + true + true + true * false
In this case, the first evaluation is true * false, then the rest of the ORs. In this particular case, the true order of evaluation of the ORs will depend on language/compiler.
If you want to force a particular order, you can always use parentheses.
if(10) it is true, but if(10 == true) is false. Can someone tell me why the first case convert the number to bool but the second case didnt?
if (10) is equivalent to if (10 != 0), whereas if (10 == true) is if (10 == 1) (since true is promoted to the value 1 of type int).
In layman's terms: Two things that both happen to satisfy some property aren't automatically the same thing.
(E.g. doughnuts and frisbees are both round, but that doesn't mean a doughnut is equal to a frisbee. Integers and booleans can both be evaluated in a boolean context, but that doesn't mean that every integer that evaluates as true is equal to every true boolean.)
if( ... )
{
// if statement
}
To execute if statement in C++, ... should have a true value.
When you wrote if( 10 ){//something useful}
I think 10 treats as int but not bool variable. The following logic should be applied then
if( 10 ) -> if( bool( 10 ) ) -> if( true )
When you write if( 10 == true ){//something useful}, according to C++ standard, there should be the following logic behind the scene
if( 10 == true ) -> if( 10 == int( true ) ) -> if( 10 == 1 ) -> if( false )
You may write something like
if( 10 != false )
or
if( !!10 == true )
also
if( ( bool ) 10 == true ) // alternatively, if( bool ( 10 ) == true )
In old C (before C99), there is no false or true, but there are 0 or non-0 values.
In modern C (from C99), there is false or true (<stdbool.h>), but they are syntactic sugar for 0 and 1, respectively.
if( 10 ) // evaluates directly since 10 is non-zero value
if( 10 == true ) -> if( 10 == 1 ) -> if( 0 )
Because they are entirely different things.
In C, anything that is NOT false is automatically true, and C has a very strict definition of false.
You can think of if(10) as if(10 != false)
and likewise if (10 == true) as if((10 == true) != false)
10 is clearly not true, in the sense that 10 is a number and true is a boolean.
When you're in an if statement, the compiler has to evaluate the condition until it reaches either a true or a false. If it does not reach a true or a false, it has to convert it to a true or a false. As a general rule, 0 evaluates to false, and everything else evaluates to true.
So if(-1) is true, as is if(234) and so on.
The expression 10 == true already evaluates to false, so no further conversion is needed. if(10) is neither true or false, so the compiler has to convert it, using our rule above, and it becomes true.
I have problem to make regExp for search panel
&& (item.get('prodAddDate') >= dateStartValue.format("Y-m-d"))
&& (item.get('prodAddDate') <= dateEndValue.format("Y-m-d"));
I'm not sure if this is task for refExp but don't have any other idea
Problem is that when I'm don't fill field with date I can't filtr data with other conditions
I was trying something like this but don't working
&& ((item.get('prodAddDate') >= dateStartValue.format("Y-m-d")) || (new RegExp(dateStartValue)).test(item.get('prodAddDate'))) &&
((item.get('prodAddDate') <= dateEndValue.format("Y-m-d")) || (new RegExp(dateEndValue)).test(item.get('prodAddDate')));
Not entirely sure what you're trying to do, but here are some pieces of information that I hope can help you to solve your problem.
Comparison operators priority
The && operator has priority over ||, which means that:
A || B && C || D
Is equivalent to:
A || (B && C) || D
Not to:
(A || B) && (C || D)
Date comparison
You can compare Date objects directly:
// example data
var d1 = new Date('2012-12-12'),
d2 = new Date('2012-12-12'),
d3 = new Date('2013-01-01');
And get the result you expect with <, >, <=, and >=:
// logical results
d1 < d3 // true
d1 < d2 // false
d2 > d3 // false
d1 <= d2 // true
d1 => d2 // true
But not with equality comparison ==:
d1 == d2 // false
// yet...
d1 <= d2 && d1 => d2 // true
Conclusion: to test if one date is before or after another one, direct comparison is OK. But, in order to test if two dates are identical, use string comparisons:
// is this the same day?
d1.format('Y-m-d') === d2.format('Y-m-d') // true
// is this the same day and hour?
d1.format('Y-m-d H:i:s') === d2.format('Y-m-d H:i:s') // true
Ext.isEmpty()
Ext.isEmpty returns true for: null, undefined and empty strings '' only.
Ext.isEmpty(null) // true
Ext.isEmpty(undefined) // true
Ext.isEmpty('') // true
Ext.isEmpty(' ') // false
Ext.isEmpty(false) // false
// etc.
That may be useful to address your empty field case:
...
&& (Ext.isEmpty(item.get('prodAddDate') || item.get('prodAddDate') >= dateStartValue)
&& (Ext.isEmpty(item.get('prodAddDate') || item.get('prodAddDate') <= dateEndValue)
Finally
What's this obsession about regex? They're useful for complex string testing/extracting, but that's all. You should probably forget about them for a while, dude ;p
I'm having trouble figuring out what this if statement is doing. This is not my code so I am simply trying to understand what the Ternary operator is doing.
if((model[STRIDE].isLogging == true ? model[STRIDE].value : g_uiStride) == g_uiStride &&
(model[NUMVERTS].isLogging == true ? model[NUMVERTS].value : NumVertices) == NumVertices &&
(model[PRIMCOUNT].isLogging == true ? model[PRIMCOUNT].value : primCount) == primCount &&
(model[STARTINDEX].isLogging == true ? model[STARTINDEX].value : startIndex) == startIndex)
{
First,
(model[STRIDE].isLogging == true ? model[STRIDE].value : g_uiStride) == g_uiStride
could be written:
(model[STRIDE].isLogging ? model[STRIDE].value : g_uiStride) == g_uiStride
the ternary
model[STRIDE].isLogging ? model[STRIDE].value : g_uiStride
checks to see if model[STRIDE].isLogging is true. If it is, it takes the value model[STRIDE].value. If not, it takes the value g_uiStride. This is then compared to g_uiStride.
So, if it isn't logging, then this portion is automatically true because g_uiStride is compared to itself. If it is logging, it is true if mode[STRIDE].value == g_uiStride
and
#1.
if (model[STRIDE].isLogging is true then
RESULT1 = (model[STRIDE].value == g_uiStride) else
RESULT1 = (g_uiStride == g_uiStride)
)
#2.
if (model[NUMVERTS].isLogging is true then
RESULT2 = (model[NUMVERTS].value == NumVertices) else
RESULT2 = (mVertices == NumVertices)
)
#3.
if (model[PRIMCOUNT].isLogging is true then
RESULT3 = (model[PRIMCOUNT].value == primCount) else
RESULT3 = (primCount == primCount)
}
#4.
if (model[STARTINDEX].isLogging is true then
RESULT4 = (model[STARTINDEX].value == startIndex) else
RESULT4 = (startIndex == startIndex)
)
if (RESULT1 && RESULT2 && RESULT3 && RESULT4) {
/* yay */
} else {
/* damn */
}
In general the ternary conditional operator uses a condition to choose between two alternatives:
condition ? first_alternative : second_alternative
In this case it is very unnecessarily complicated by comparing to true and one object to itself
if((model[STRIDE].isLogging == true ? model[STRIDE].value : g_uiStride) == g_uiStride
This can be reduced to
if((model[STRIDE].isLogging ? model[STRIDE].value : g_uiStride) == g_uiStride
which is also equivalent to
if (model[STRIDE].value == g_uiStride || !model[STRIDE].isLogging
telling us that either value is equal to some global value, or we don't care because we are not logging anyway.
blah = (model[STRIDE].isLogging == true ? model[STRIDE].value : g_uiStride)
is the same as
if (model[STRIDE].isLogging) {
blah = model[STRIDE].value ;
} else {
blah = g_uiStride;
}
The ternary operator is as follows:
(condition) ? value_for_true_condition : value_for_false_condition
(model[STRIDE].isLogging == true ? model[STRIDE].value : g_uiStride) first checks to see if the isLogging == true, the (condition). If the condition is true the model[STRIDE].value value is used, if not true the g_uiStride value is used.
The statement as a whole checks the values on all those members of model, but only if the member .isLogging == true. Otherwise it uses the default value. Note that this statement will always be true if all members have .isLogging variable set to false.