int H;
int M;
int SleepH;
int SleepM;
cout << NumActivities[2][0];
cin >> H >> M;
cout << NumActivities[2][1];
cin >> SleepH >> SleepM;
int SubtractM;
int SubtractH;
if (H<=12)
{
int MH=24;
int MM=60;
SubtractH= MH-H;
SubtractM = MM-M;
}
if (SleepM==00)
{
int SleepM= SleepM+60;
int TimeLeftH;
TimeLeftH= SleepH-SubtractH;
int TimeLeftM;
TimeLeftM= SleepM-SubtractM;
int F;
F=TimeLeftM/60;
int DoThisZ;
DoThisZ= TimeLeftH + F;
float Normal = Normal + DoThisZ;
cout<<Normal;
}
}
}
Above is my program. It's unfinished but when doing runs the program keeps ending early right after it outputs NumActivities[2][1] on line 64. I can't find any way to stop this and taking away the loop doesn't change anything.
I expect the program to let me enter the the variables H,M,SleepH and SleepM and then show me the result but it just closes after displaying NumActivities[2][1] without letting me enter the variables.
When the program asks you "What's your bedtime?(In 24 hour format):", if your answer contains colon (:), it takes input for your next question - "How long do you sleep?:" - as well.
This is because in C++, comma-separators are not part of a number, as decimal points aren't for integers, so as soon as the operation finds either the comma or the point, the extraction operation ends, leaving that character as the next to be extracted. Subsequent extraction operations find that character as the first one to be extracted, so they all return.
Enter your first answer as something like "11 30" - space between the numbers, not colon. Then, the program is supposed to take input for your next question as well.
Just to give an advice, you are wasting your iteration numbers 0,1,2,4,5. So, you can simply take away the for loop.
Related
I am writing a code that tally when an integer data type or character is entered.
int numero,
countInteger = 0;
countCharacter = 0;
while ( 1 ) {
try {
cin >> numero;
cout << numero;
throw numero;
} catch (...) {
countCharacter++;
cout << "Error";
}
}
If I entered Integer, counter in "countInteger" (but not show it in the code). If I enter a character, it is aa exception and recorded in "countCharacter".
But when I run the code generates an infinite loop and does not allow me to re-enter again. They could help me please. Guide me, you may have a bad concept.
When you try to read an integer, and you give something that's not an integer as input, there are two things happening: The first is that the stream gets its failbit set, the second things that happens is that the input is not extracted. So next iteration you read the same input again, and again and again...
I suggest another tactic: Read as a character, then see if it is a digit, an alphabetic character, or something else completely. Optionally, if you need the actual full number, read as a string, and try to convert to an integer.
A clarification: Input using std::cin is buffered. When you use the input operator >> then std::cin extracts characters from the buffer. If you try to read a number, but the first character in the buffer is not a digit, then the input operator will fail, and leave the character in the buffer.
Simple (hopefully) example:
Lets say you have this code
int number;
std::cin >> number;
std::cin >> number;
std::cin >> number;
As input for that part of the code, you enter
123abc
The first input will read 123 from the input, and stop at the letter, leaving the input as
abc
Now we come to the second input, and the code will see that the first character is not a digit, so it will set the failbit in the stream and leave the input as is:
abc
Then with the third input, the exact same thing as in the second happen.
Now imagine this was in a loop instead, the input operator >> will iteration after iteration see the non-digit input an promptly return, effectively giving you an infinite loop.
Now for a clarification of my suggestion... Depending on the goals and requirements of the program, you can instead read into a character and use the character classification functions to see what types you have.
Something like
int countDigit = 0;
int countCharacter = 0;
char ch;
while (std::cin >> ch)
{
if (std::isdigit(ch))
++countDigit;
else if (std::isalpha(ch))
++countCharacter;
else
{
// Not a digit or an alphabetic character
// I.e. newlines, spaces, control characters, etc.
}
}
Finally a note about using exceptions for this: Most people would consider it bad. Exceptions are for exceptions, exceptional cases, not as part of the normal flow of the program. Throwing an exception is expensive and disrupts the normal flow. Only use them for exceptional things, like errors.
I'll be flat out honest, this is a small snippet of code I need to finish my homework assignment. I know the community is very suspicious of helping students, but I've been racking my head against the wall for the past 5 hours and literally have accomplished nothing on this assignment. I've never asked for help on any assignments, but none have given me this much trouble.
All I'm having trouble with is getting the program to strip the leading whitespace out. I think I can handle the rest. I'm not asking for a solution to my overall assignment, just a nudge on this one particular section.
I'll post the full assignment text here, but I am NOT posting it to try to get a full solution, I'm only posting it so others can see the conditions I have to work with.
"This homework will give you more practice in writing functions and also how numbers are read into a variable. You need to write a function that will read an unsigned integer into a variable of type unsigned short int. This will have a maximum value of 65535, and the function needs to take care of illegal numbers. You can not use "cin >>", inside the function.
The rules for numeric input are basically as follows:
1) skip all leading white spaces
2) first character found must be numeric else an error will occur
3) numeric characters are then processed one at a time and combine with number
4) processing stops when non-numeric found
We will follow these rules and also add error handling and overflow. If an illegal entry is made before a numeric than an error code of "1" will be sent back, if overflow occurs, that is number bigger then 65535, then error code of "2" will be sent back. If no error then "0" is sent back.
Make sure the main function will continue to loop until the user enters a “n” or “N” for NO, the main should test the error code returned from the function called “ReadInt” and display appropriate error messages or display the number if there is no error. Take care in designing the “ReadInt” function, it should be value returning and have a reference parameter. The function needs to process one character at a time from the input buffer and deal with it in a correct fashion. Once the number has been read in, then make sure the input buffer is empty, otherwise the loop in main may not work correct. I know this is not how the extraction works, but lets do it this way.
You do not need to turn in an algorithm with this assignment, but I would advise you to write one. And the debugger may prove helpful as well. You are basically rewriting the extraction operator as it works on integers."
A majority of my code won't make sense as I've been deleting things and adding things like crazy to try everything I can think of.
#include <iostream>
#include <CTYPE.h>
using namespace std;
int ReadInt (unsigned short int &UserIn);
int main()
{
int Error;
unsigned short int UserInput;
char RepeatProgram;
do
{
Error=ReadInt(UserInput);
if (Error==0)
cout << "Number is " << UserInput << endl;
else if (Error==1)
cout << "Illegal Data Entry\n";
else if (Error==2)
cout << "Numerical overflow, number too big\n";
cout << "Continue? n/N to quit: ";
cin >> RepeatProgram;
cout << endl;
} while (RepeatProgram!='N' && RepeatProgram!='n');
}
int ReadInt (unsigned short int &UserIn)
{
int Err=0;
char TemporaryStorage;
long int FinalNumber=0;
cout << "Enter a number: ";
//cin.ignore(1000, !' '); this didn't work
cin.get(TemporaryStorage);
cout << TemporaryStorage;//I'm only displaying this while I test my ideas to see if they are working or not, before I move onto the the next step
cout << endl;
return Err;
}
I really appreciate any help I may get and hope I don't give the impression that I'm looking for a full free solution to the whole problem. I want to do this on my own, I'm just lot on this beginning.
As a preface, I want to state that this is a question made by a student, but unlike most of their type, it is a quality question that merits a quality answer, so I'll try to do it ;). I won't try to just answer your concrete question, but also to show you other slight problems in your code.
First of all, let's analyze your code step by step. More or less like what a debugger would do. Take your time to read this carefully ;)...
#include <iostream>
#include <CTYPE.h>
Includes headers <iostream> and <ctype.h> (the uppercase works because of some flaws/design-decisions of NTFS in Windows). I'ld recommend you to change the second line to #include <cctype> instead.
using namespace std;
This is okay for any beginner/student, but don't get an habit of it! For the purposes of "purity", I would explicitly use std:: along this answer, as if this line didn't existed.
int ReadInt (unsigned short int &UserIn);
Declares a function ReadInt that takes a reference UserIn to type unsigned short int and returns an object of type int.
int main()
{
Special function main; no parameters, returns int. Begin function.
int Error;
unsigned short int UserInput;
char RepeatProgram;
Declares variables Error, UserInput, and RepeatProgram with respective types int, unsigned short int, and char.
do
{
Do-while block. Begin.
Error=ReadInt(UserInput);
Assign return value of ReadInt of type int called with argument UserInput of type int& to variable Error of type unsigned short int.
if (Error==0)
std::cout << "Number is " << UserInput << endl;
If Error is zero, then print out UserInput to standard output.
else if (Error==1)
std::cout << "Illegal Data Entry\n";
else if (Error==2)
std::cout << "Numerical overflow, number too big\n";
Otherwise, if an error occurs, report it to the user by means of std::cout.
std::cout << "Continue? n/N to quit: ";
std::cin >> RepeatProgram;
Query the user if he/she wants to continue or quit. Store the input character in RepeatProgram of type char.
std::cout << std::endl;
Redundant, unless you want to add padding, which is probably your purpose. Actually, you're better off doing std::cout << '\n', but that doesn't matters too much.
} while (RepeatProgram!='N' && RepeatProgram!='n');
Matching expression for the do-while block above. Repeat execution of the given block if RepeatProgram is neither lower- or uppercase- letter N.
}
End function main. Implicit return value is zero.
int ReadInt (unsigned short int &UserIn)
{
Function ReadInt takes a reference UserIn to unsigned short int and returns an object of type int. Begin function.
int Err=0;
char TemporaryStorage;
long int FinalNumber=0;
Declares variables Err, TemporaryStorage, and FinalNumber of respective types int, char, and long int. Variables Err and FinalNumber are initialized to 0 and 0, respectively. But, just a single thing. Didn't the assignment said that the output number be stored in a unsigned short int? So, better of this...
unsigned short int FinalNumber = 0;
Now...
std::cout << "Enter a number: ";
//std::cin.ignore(1000, !' '); this didn't work
Eh? What's this supposed to be? (Error: Aborting debugger because this makes no logic!**). I'm expecting that you just forgot the // before the comment, right? Now, what do you expect !' ' to evaluate to other than '\0'? istream::ignore(n, ch)will discard characters from the input stream until either n characters have been discarded, ch is found, or the End-Of-File is reached.
A better approach would be...
do
std::cin.get(TemporaryStorage);
while(std::isspace(TemporyStorage));
Now...
std::cin.get(TemporaryStorage);
This line can be discarded with the above approach ;).
Right. Now, where getting into the part where you obviously banged your head against all solid objects known to mankind. Let me help you a bit there. We have this situation. With the above code, TemporaryStorage will hold the first character that is not whitespace after the do-while loop. So, we have three things left. First of all, check that at least one digit is in the input, otherwise return an error. Now, while the input is made up of digits, translate characters into integers, and multiply then add to get the actual integer. Finally, and this is the most... ahem... strange part, we need to avoid any overflows.
if (!std::isdigit(TemporaryStorage)) {
Err = 1;
return Err;
}
while (std::isdigit(TemporaryStorage)) {
unsigned short int OverflowChecker = FinalNumber;
FinalNumber *= 10; // Make slot for another digit
FinalNumber += TemporaryStorage - '0'; '0' - '0' = 0, '1' - '0' = 1...
// If an unsigned overflows, it'll "wrap-around" to zero. We exploit that to detect any possible overflow
if (FinalNumber > 65535 || OverflowChecker > FinalNumber) {
Err = 2;
return Err;
}
std::cin.get(TemporaryStorage);
}
// We've got the number, yay!
UserIn = FinalNumber;
The code is self-explanatory. Please comment if you have any doubts with it.
std::cout << TemporaryStorage;//I'm only displaying this while I test my ideas to see if they are working or not, before I move onto the the next step
cout << endl;
return Err;
Should I say something here? Anyway, I already did. Just remember to take that std::couts out before showing your work ;).
}
End function ReadInt.
You can skip leading whitespace from a stream using std::ws. For example:
std::cin >> std::ws;
This use of >> just invokes the manipulator std::ws on the stream. To meet the teacher's requirements you can invoke it directly:
std::ws(std::cin);
Formatted input automatically skips whitespace. Note that should also always check whether input was successful:
if (std::cin.get(TemporaryStorage)) {
...
}
I have these 2 codes:
char a[256];
cin>>a;
cout<<a;
and
char a[256];
cin.get(a,256);cin.get();
cout<<a;
and maybe, relative to the second one without cin.get();
char a[256];
cin.get(a,256);
cout<<a;
My question is (first one) : for a char array, what should i use? cin or cin.get()? And why should i use cin.get(); with no parameter after my char initialisation?
And my second question is: my c++ teacher taught me to use every time cin.get() for initialisation chars and AFTER every initialisation char array or int array or just int or whatever, to again put cin.get(); after it. That's what i wanted to ask initially.
So, now i got these 2:
In this case, without cin.get() after the integer initialisation, my program will break and i can't do anymore my char initialisation.
int n;
cin>>n;
char a[256];
cin.get(a,256); cin.get(); // with or without cin.get();?
cout<<a;
And the correct one:
int n;
cin>>n; cin.get();
char a[256];
cin.get(a,256); cin.get(); // again, with or without?
cout<<a;
So, what's the matter? Please someone explain for every case ! Thank you.
They do different things, so choose whichever does what you want, or the better alternatives given below.
The first cin>>a; reads a single word, skipping over any leading space characters, and stopping when it encounters a space character (which includes the end of the line).
The second cin.get(a,256);cin.get(); reads a whole line, then consumes the end-of-line character so that repeating this will read the next line. cin.getline(a,256) is a slightly neater way to do this.
The third cin.get(a,256) reads a whole line but leaves the end-of-line character in the stream, so that repeating this will give no more input.
In each case, you'll get some kind of ill behaviour if the input word/line is longer than the fixed-size buffer. For that reason, you should usually use a friendlier string type:
std::string a;
std::cin >> a; // single word
std::getline(std::cin, a); // whole line
The string will grow to accommodate any amount of input.
The problem, most likely, is in the way you enter the values later on. The cin.get() after every initialization is there to "grab" the newline character that gets put in the stream every time you press enter.
Say you start entering your values like this:
2
a b c d...
Assuming you have pressed enter after 2, the newline character was also put on the stream. When you call cin.get() after that, it will grab and discard the newline character, allowing the rest of your code to properly get the input.
To answer your first question, for an array, you should use cin.get instead of the overloaded operator >> cin>> as that would only grab a single word, and it would not limit the amount of characters grabbed, which could lead to an overflow and data corruptions / program crashing.
On the other hand, cin.get() allows you to specify the maximum number of characters read, preventing such bugs.
For a char array use cin.get() because it counts whitespace whereas cin does not. More importantly, cin.get() sets the maximum number of characters to read. For example:
char foo[25]; //set maximum number of characters
cout << "Please type in characters for foo" << endl;
cin.get(foo,25);
cout << ' ' << foo;
In this case, you can only type in 24 characters and a null terminator character \0.
I hope this answers your first question.
I would personally use a string.
I have this code snippet that is supposed to test whether the user enters an integer or not. This works if the user enters letters, but not decimals and I'm left wondering why that is. Here's my code snippet:
Student student;
int id;
while(!(cin >> id))
{
cout << "\nERROR: Please enter a Positive Whole Number" << endl;
cin.clear();
cin.ignore ();
cout << "Enter Student ID: ";
}
Entering A will make it iterate through the while loop, but if I enter 12.5 it drops out of the while loop and keeps going. Isn't it testing whether it will parse to integer or not? Why is it accepting 12.5 but not characters?
cin>>id will succeed as long as it finds something it can convert to an int ("12", in this case). When it reaches something it can't convert, it stops, but if it's read an int already, that counts as success.
To check that everything it read was digits, you might want to do something like using std::getline to read a line of input into a string, then use std::isdigit to test whether those are all digits. Testing a conversion to int (by itself) will only tell you that it found something that could be read as an integer, but won't tell you if that was followed by other things that couldn't be converted to an int.
I rewrote this loop in several ways, with nested Ifs and do whiles, yet behavior is the same. It behaves as expected as long as the user does not enter a character or a string. Once the user does it just goes on spinning the loop until I CTRL+C it.
From what I have researched, when a variable is a number and the user inputs a char or a string, they just get converted into their ASCII numbers, in which case the while check should work. The number should be larger than allowed and the user should be prompted for a new value right? Why does it keep looping infinitely?
Width is declared as a float.
void setWidth ()
{
std::cout << "\nPlease enter the width (use numbers greater than 0 and no greater than 20.0).\n";
std::cin >> width;
while (width <= 0 || width > 20)
{
std::cin.clear();
std::cin.ignore();
std::cout << "You have entered a number outside of the allowed range.\nPlease enter a number greater than 0 and no greater than 20.\n";
std::cin >> width;
}
}
Like I said, for numbers it works great, doubles, negatives, whatever. But something like "asdf" or "a" will put it in infinitely spinning loop.
It seems like I've tried everything. Why does this happen? I mean I know why it loops, it's because the number is not between 0 and 20, but why does it not ask user for input? I do clear the buffer.
The line std::cin >> width; fails because the input isn't a number. It also doesn't consume any of the input, so you are stuck in an infinite loop.
To avoid this, you should read the input using std::getline(), then try to convert it (std::ostringstream is one option), handling and reporting failures accordingly.
The default for cin.ignore() is to ignore just a single character.
If you want to ignore longer strings, you have to add extra parameters for that, perhaps cin.ignore(1000, '\n') which skips up to 1000 characters or the next newline (whichever comes first).
cin::clear() "Sets a new value for the error control state" 1, but the remaining input is still here and still read.
Then I guess the actual behavior depends on the compiler since when I compile it with g++ 4.6.3 and type the input "abc", it only loops three times and then wait for another input.
To empty the cin buffer you may rather see How do I flush the cin buffer?
Try checking the failbit on cin
Ok, thanks for all the help guys... I finally managed to get it to work with cin (not getline), by doing exactly what ive been doing, except I made a clearBuffer() function. So instead of clearing the buffer from within the getWidth function, the getWidth function calls another function.. thereby leaves the getWidth function to execute some code... then comes back to run the rest of it...
For some reason when it goes outside of the function it works fine and strings and chars trigger the error.. but if the cin.clear and cin.ignore are kept within the function then I have that problem.
So the final code looks like this.
void clearBuffer()
{
std::cin.clear();
std::cin.ignore(80, '\n'); //Ignore the first 80 characters up to an Enter character.
}
void setWidth ()
{
std::cout << "\n\t\tPlease enter the width.\n(use numbers greater than 0 and no greater than 20.0).\n";
float temp = NULL; //Using temp here so that we dont write invalid characters to an actual variable.
std::cin >> temp;
clearBuffer();
while (temp <= 0 || temp > 20)
{
std::cout << "\nERROR: You have entered width outside of the allowed range.\nPlease enter a number greater than 0 and no greater than 20.\n";
std::cin >> temp;
clearBuffer();
}
if(temp > 0 && temp <= 20)
width=temp;
}