I'm using the Code::Blocks IDE and whenever I try to build the file this code brings up an error:
{
cin >> input ;
locale loc;
for (string::size_type i=0; i<input.length(); ++i)
input[i] = tolower(input[i],loc);}
{
if (input == "not")
"" != "";
else if (input == "and")
"" && "";
else if (input == "or")
"" || "";
else if (input == "yes")
input = true;
else if (input == "no")
input = false;
}
The error occurs where I try to make the word "no" equal to the Boolean operator false.
This brings up this error:
Projects\Samantha\main.cpp|40|error: ambiguous overload for 'operator=' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and 'bool')|
Now I've tried searching for this problem but I haven't been able to find anything to help me. If someone could please help me to figure what the problem is and how I can fix it I would be very appreciative.
The problem is that you are trying to assign a Boolean to a string.
You have two options here
Create a bool variable where you will store your false value
assign a string literal instead of a boolean input = "false";
Please note that the first three ifs are doing nothing since you are performing logical operations on empty string literals and not storing the result anywhere.
I'd also recommend to avoid using if() conditions without following braces since that is an error-prone, difficult to maintain and difficult to read approach.
else if (input == "yes")
{
booleanVariable = true;
}
Related
I am facing an issue with arduino, since I want to change the state of my device using an enum, but it doesn't seeem to work, my code looks like below. I am not entirely sure where it goes wrong, I think as well that the comparison between settingTo and toP2P could be wrong?
Thanks in advance!
String toP2P = "503250"
String toABP = "414250";
String settingTo = LoRa_Tx.dataRX.substring(indx);
if( settingTo == toP2P ) {
//switching to P2P
Serial.println("current mode 1 "+(String) LoRa_Tx.current_modeRxTx);
if(LoRa_Tx.current_modeRxTx != LoRa_Tx.LoRaMod){
LoRa_Tx.current_modeRxTx = LoRa_Tx.LoRaMod;
}
} else if(settingTo == toABP){
//switching to ABP
if(LoRa_Tx.current_modeRxTx != LoRa_Tx.LoRaWan){
LoRa_Tx.current_modeRxTx = LoRa_Tx.LoRaWan;}
}
}
My class has the enum defined as
typedef enum modeRxTx{LoRaMod, LoRaWan, Idle} ;
modeRxTx current_modeRxTx = Idle;
In general, you should avoid the String class, as it will eventually cause problems. However, given that the LoRa_Tx appears to have a String member, here is one way to watch for those two modes:
if ((indx > -1) && (LoRa_Tx.dataRx.length() >= indx+5)) {
const char *settingTo = &LoRa_Tx.dataRx.c_str()[ indx ];
if ( strncmp_P( settingTo, PSTR("503250"), 6 ) == 0 ) {
//switching to P2P
Serial.print( F("current mode 1 ") ); // <-- saves RAM!
Serial.println( LoRa_Tx.current_modeRxTx );
if(LoRa_Tx.current_modeRxTx != LoRa_Tx.LoRaMod) {
LoRa_Tx.current_modeRxTx = LoRa_Tx.LoRaMod;
}
} else if ( strncmp_P( settingTo, PSTR("414250"), 6 ) == 0 ) {
//switching to ABP
if(LoRa_Tx.current_modeRxTx != LoRa_Tx.LoRaWan) {
LoRa_Tx.current_modeRxTx = LoRa_Tx.LoRaWan;
}
}
}
Instead of creating a substring, it just makes a pointer to the actual characters of data_Rx. The c_str() function returns a pointer to the first character (zero-based index) or the String, and the [ indx ] is the first of the mode number characters. Finally, the & is a pointer to the first mode number character.
Next, it uses a standard library function, strncmp_P (documented here), to compare those mode number characters with the modes you are looking for, and it only compares up to 6 characters. You don't say if there's a delimiter after "503250", so I don't know if "50325076" is possible and should be rejected.
The strncmp_P expects to get a PROGMEM string as the second argument, not just a const char *, so that's what the PSTR macro does. This saves RAM because the PSTR will be stored and compared from FLASH memory (aka PROGMEM). The Serial.print statements should use the F() macro for the same reason.
I'm writing a for loop for a project that prompts the user to input a number and keeps prompting, continually adding the numbers up. When a string is introduced, the loop should stop. I've done it with a while loop, but the project states that we must do it with a for loop also. The problem is that the prompt keeps running even when 'a = false'. Could someone explain javascript's thinking process? I want to understand why it keeps running back through the loop even though the condition isn't met. Thank you
var addSequence2 = function() {
var total = 0;
var a;
for (; a = true; ) {
var input = prompt("Your current score is " +total+ "\n" + "Next number...");
if (!isNaN(input)) {
a = true;
total = +total + +input;
}
else if (isNaN(input)) {
a = false;
document.write("Your total is " + total);
}
}
};
There is a difference between a = true and a == true.
Your for-loop is basically asking "can I set 'a' to true?", to which the answer is yes, and the loop continues.
Change the condition to a == true (thus asking "Is the value of 'a' true?")
To elaborate, in most programming languages, we distinguish between assignment ("Make 'x' be 4") and testing for equality ("Is 'x' 4?"). By convention (at least in languages that derive their syntax from C), we use '=' to assign/set a value, and '==' to test.
If I'm understanding the specification correctly (no guarantee), what happens here is that the condition condenses as follows:
Is (a = true) true?
Complete the bracket: set a to true
Is (a) true? (we just set it to true, so it must be!)
Try using the equal to operator, i.e. change
for (; a = true; ) {
to
for (; a == true; ) {
You should use a == true instead of a = true......= is an assignment operator
for (; a = true; ), you are assigning the value to the variable "a" and it will always remain true and will end up in infinite loop. In JavaScript it should a===true.
I suspect you want your for to look like this :
for(;a==true;)
as a=true is an assignment, not a comparison.
a == true. The double equal sign compares the two. Single equal assigns the value true to a so this always returns true.
for (; a = true; ) <-- this is an assignation
for (; a == true; ) <-- this should be better
Here's your fixed code :
var addSequence2 = function() {
var total = 0;
var a = true;
for(;Boolean(a);) {
var input = prompt("Your current score is " +total+ "\n" + "Next number...");
if (!isNaN(input)) {
total = total + input;
}
else{
a = false;
document.write("Your total is " + total);
}
}
};
I am trying to write some logic to determine if all values of a certain property of an object in a collection are numeric and greater than zero. I can easily write this using ForEach but I'd like to do it using Linq to Object. I tried this:
var result = entity.Reports.Any(
x =>
x.QuestionBlock == _question.QuestionBlock
&& (!string.IsNullOrEmpty(x.Data)) && Int32.TryParse(x.Data, out tempVal)
&& Int32.Parse(x.Data) > 0);
It does not work correctly. I also tried this, hoping that the TryParse() on Int32 will return false the first time it encounter a string that cannot be parsed into an int. But it appears the out param will contain the first value string value that can be parsed into an int.
var result = entity.GranteeReportDataModels.Any(
x =>
x.QuestionBlock == _question.QuestionBlock
&& (!string.IsNullOrEmpty(x.Data)) && Int32.TryParse(x.Data, out tempVal));
Any help is greatly appreciated!
If you want to test if "all" values meet a condition, you should use the All extension method off IEnumerable<T>, not Any. I would write it like this:
var result = entity.Reports.All(x =>
{
int result = 0;
return int.TryParse(x.Data, out result) && result > 0;
});
I don't believe you need to test for an null or empty string, because int.TryPrase will return false if you pass in a null or empty string.
var allDataIsNatural = entity.Reports.All(r =>
{
int i;
if (!int.TryParse(r.Data, out i))
{
return false;
}
return i > 0;
});
Any will return when the first row is true but, you clearly say you would like to check them all.
You can use this extension which tries to parse a string to int and returns a int?:
public static int? TryGetInt(this string item)
{
int i;
bool success = int.TryParse(item, out i);
return success ? (int?)i : (int?)null;
}
Then this query works:
bool all = entity.Reports.All(x => {
if(x.QuestionBlock != _question.QuestionBlockint)
return false;
int? data = x.Data.TryGetInt();
return data.HasValue && data.Value > 0;
});
or more readable (a little bit less efficient):
bool all = entityReports
.All(x => x.Data.TryGetInt().HasValue && x.Data.TryGetInt() > 0
&& x.QuestionBlock == _question.QuestionBlockint);
This approach avoids using a local variable as out parameter which is an undocumented behaviour in Linq-To-Objects and might stop working in future. It's also more readable.
Quoted from wiki:
void term(void) {
factor();
while (sym == times || sym == slash) {
getsym();
factor();
}
}
void expression(void) {
if (sym == plus || sym == minus)
getsym();
term();
while (sym == plus || sym == minus) {
getsym();
term();
}
}
It's using void return type for each rule,
in that case, how can one know whether a specific branch fails or succeeds?
IMO, each rule should use a boolean return type to indicate whether this branch fails or succeeds.
Is this correct?
The example uses a model where a special "error" routine is responsible for reporting errors, but you could certainly formulate the parser as a function that returned "true" if the input represented a valid input and "false" otherwise. It's just two different styles.
How can we do validation for percentage numbers in textbox .
I need to validate these type of data
Ex: 12-3, 33.44a, 44. , a3.56, 123
thanks in advance
sri
''''Add textbox'''''
<asp:TextBox ID="PERCENTAGE" runat="server"
onkeypress="return ispercentage(this, event, true, false);"
MaxLength="18" size="17"></asp:TextBox>
'''''Copy below function as it is and paste in tag..'''''''
<script type="text/javascript">
function ispercentage(obj, e, allowDecimal, allowNegative)
{
var key;
var isCtrl = false;
var keychar;
var reg;
if (window.event)
{
key = e.keyCode;
isCtrl = window.event.ctrlKey
}
else if (e.which)
{
key = e.which;
isCtrl = e.ctrlKey;
}
if (isNaN(key)) return true;
keychar = String.fromCharCode(key);
// check for backspace or delete, or if Ctrl was pressed
if (key == 8 || isCtrl)
{
return true;
}
ctemp = obj.value;
var index = ctemp.indexOf(".");
var length = ctemp.length;
ctemp = ctemp.substring(index, length);
if (index < 0 && length > 1 && keychar != '.' && keychar != '0')
{
obj.focus();
return false;
}
if (ctemp.length > 2)
{
obj.focus();
return false;
}
if (keychar == '0' && length >= 2 && keychar != '.' && ctemp != '10') {
obj.focus();
return false;
}
reg = /\d/;
var isFirstN = allowNegative ? keychar == '-' && obj.value.indexOf('-') == -1 : false;
var isFirstD = allowDecimal ? keychar == '.' && obj.value.indexOf('.') == -1 : false;
return isFirstN || isFirstD || reg.test(keychar);
}
</script>
You can further optimize this expression. Currently its working for all given patterns.
^\d*[aA]?[\-.]?\d*[aA]?[\-.]?\d*$
If you're talking about checking that a given text is a valid percentage, you can do one of a few things.
validate it with a regex like ^[0-9]+\.?[0-9]*$ then just convert that to a floating point value and check it's between 0 and 100 (that particular regex requires a zero before the decimal for values less than one but you can adapt it to handle otherwise).
convert it to a float using a method that raises an exception on invalid data (rather than just stopping at the first bad character.
use a convoluted regex which checks for valid entries without having to convert to a float.
just run through the text character by character counting numerics (a), decimal points (b) and non-numerics (c). Provided a is at least one, b is at most one, and c is zero, then convert to a float.
I have no idea whether your environment support any of those options since you haven't actually specified what it is :-)
However, my preference is to go for option 1, 2, 4 and 3 (in that order) since I'm not a big fan of convoluted regexes. I tend to think that they do more harm than good when thet become to complex to understand in less than three seconds.
Finally i tried a simple validation and works good :-(
function validate(){
var str = document.getElementById('percentage').value;
if(isNaN(str))
{
//alert("value out of range or too much decimal");
}
else if(str > 100)
{
//alert("value exceeded");
}
else if(str < 0){
//alert("value not valid");
}
}