I wish to take inputs from console where the number of inputs are not known. All i know is that they are less then or equal to 10.
I wrote this code but it evaluates the last value twice.
int x;
do{
cin>>x;
cout<<check(x)<<"\n";
}while(std::cin);
The inputs are in this form:
12
2
45
As #LightnessRacesinOrbit commented, it's while(!eof) bug again. You should check the stream state after reading from it, not before.
You can use cin>>x in the while-condition and apply a special value (i.e. anything not a number) as the end flag like this:
while (cin >> x)
{
// got a value
}
You may use istream::geline.
char input[1024]
std::cin.getline (input,1024);
After you read the line, you have to split it by white-spaces as delimiter. Just ignore 11th split onwards. And you may apply atoi or similar functions on the splits (some_split.c_str()) to get the numeric values
Related
I was given a question where the input will be like:
10 8
4 9
6 12
5 4
3
1
Here I don't know the number of lines that contains 2 integers. Those sets of 2 integers will be taken into an array. But when the program encounters "3", it will start taking input in another array.
I have tried this with
while(cin>>a>>b){ //some porcess with a and b }
but it doesn't work because it recognizes 3 and 1 as another set of two integers. Please help me to solve this problem.
cin >> a >> b skips not only spaces, but any delimeter characters too ('\n', '\t', ' ').
Here you actually may want to read input line-by-line and then check if there are two integers or one. Consider use of std::getline for retrieving each line of text. Then you can use read string as std::istream (like in example in the link above) and read from it with counting, how many numbers you read totally.
So think about your problem. Essentially it is, read one line at a time, and if it contains two numbers do one thing, but if it contains one number do something else.
But the code you have written reads numbers not lines. That is where the problem is.
Instead write your code to read only line at a time, analyse that line to see if it contains one or two numbers (or something else) and then proceed from there.
What you need is the ability to read a line of text into a string, and then read from that string into your numbers. To do that you use an istringstream. Something like this
#include <iostream>
#include <sstream>
#include <string>
int a, b;
string s;
getline(cin, s); // read one line from standard input
istringstream line(s); // put that string to a stream we can read from
if (line >> a) // try and read the first number from the stream
{
// got the first number
if (line >> b) // try and read the second number from the stream
{
// got the second number
...
}
else
{
// only one number
...
}
}
else
{
// didn't get any numbers, some sort of error
...
}
I am trying to read the last integer from an input such as-
100 121 13 ... 7 11 81
I'm only interested in the last integer and hence want to ignore all
previous integers.
I thought of using cin.ignore but that won't work here due to
unknown integers (100 is of 3 digits, while 13 is of 2 digits & so on)
I can input integer by integer using a loop and do nothing with them. Is there a better way?
It all depends on the use case that you have.
Reading a none specified number of integers from std::cin is not as easy at it may seem. Because, in contrast to reading from a file, you will not have an EOF condition. If you would read from a file stream, then it would be very simple.
int value{};
while (fileStream >> value)
;
If you are using std::cin you could try pressing CTRL-D or CTRL-Z or whatever works on your terminal to produce an EOF (End Of File) condition. But usually the approach is to use std::getline to read a complete line until the user presses enter, then put this line into a std::istringstream and extract from there.
Insofar, one answer given below is not that good.
So, next solution:
std::string line{};
std::getline(std::cin, line);
std::istringstream iss{line};
int value{};
while (iss >> value)
;
You were asking
Is there a better way?
That also depends a little. If you are just reading some integers, then please go with above approach. If you would have many many values, then you would maybe waste time by unnecessarily converting many substrings to integers and loose time.
Then, it would be better, to first read the complete string, then use rfind to find the last space in the string and use std::stoi to convert the last substring to an integer.
Caveat: In this case you must be sure (or check with more lines of code) that there are no white space at the end and the last substring is really a number. That is a lot of string/character fiddling, which can most probably avoided.
So, I would recommend the getline-stringstream approach.
You can try this simple solution for dynamically ignoring rest of the values except the last given in this problem as shown:
int count = 0;
int values, lastValue; // lastValue used for future use
std::cout << "Enter your input: ";
while (std::cin >> values) {
lastValue = values; // must be used, otherwise values = 0 when loop ends
count++;
}
std::cout << lastValue; // prints
Note: A character must be required to stop the while(), hence it's better put a . at last.
Output example
Enter your input: 3 2 4 5 6 7.
7
Try this:
for( int i=0; i<nums_to_ignore; i++) {
int ignored;
std::cin >> ignored;
}
Not sure if the title is properly worded, but what I am trying to ask is how would you signify the end of input for an array using newline. Take the following code for example. Not matter how many numbers(more or less) you type during the input for score[6], it must take 6 before you can proceed. Is there a method to change it so that an array can store 6 or 100 variables, but you can decide how many variables actually contain values. The only way I can think of doing this is to somehow incorporate '\n', so that pressing enter once creates a newline and pressing enter again signifies that you don't want to set any more values. Or is something like this not possible?
#include <iostream>
using namespace std;
int main()
{
int i,score[6],max;
cout<<"Enter the scores:"<<endl;
cin>>score[0];
max = score[0];
for(i = 1;i<6;i++)
{
cin>>score[i];
if(score[i]>max)
max = score[i];
}
return 0;
}
To detect "no input was given", you will need to read the input as a input line (string), rather than using cin >> x; - no matter what the type is of x, cin >> x; will skip over "whitespace", such as newlines and spaces.
The trouble with reading the input as lines is that you then have to "parse" the input into numbers. You can use std::stringstream or similar to do this, but it's quite a bit of extra code compared to what you have now.
The typical way to solve this kind of problem, however, is to use a "sentry" value - for example, if your input is always going to be greater or equal to zero, you can use -1 as the sentry. So you enter
1 2 3 4 5 -1
This would reduce the amount of extra code is relatively small - just check if the input is -1, such as
while(cin >> score[i] && score[i] >= 0)
{
...
}
(This will also detect end-of-file, so you could end the input with CTRL-Z or CTRL-D as appropriate for your platform)
I'm working on a project where I need to input floats and assign them to a vector, I'm doing so like this:
//Input to temporary float
while (cin >> input)
{
//Assign temporary float to vector<float>
a.math_grades.push_back(input);
}
This works, but to end the while loop I have to input a letter. How can I input to a vector and be able to end that input by simply pressing enter?
Thanks in advance! :D
-- Connor
Assuming that you want to indicate the end of a list with a blank line so that you can then move on to inputting other data, the end-of-file indicator won't help you much.
In that case, you should use std::getline to read a line at a time, end the loop on error OR empty string. Inside the loop you'll convert each non-empty string to a float. boost::lexical_cast is a good choice for the latter operation, so is strtof
I have a program that reads a credit card number. I want to add in something that makes sure that 16 numbers are added in, no letters, and as many spaces as wanted (although they don't count towards numbers). Is there a function or set of functions to do this, or should I just make a bunch of while and if loops that use isdigit() and isalpha() that goes through the array one element at a time?
char cardNum[32];
cout << "Enter credit card number: ";
cin.getline(cardNum, 32); //Read in the entire line for the name
There are numerous things you could do. One idea is to use std::find_if with a custom predicate. For example:
bool IsCharIllegal(char ch)
{
// return true or false based on whatever your exact requirements are
}
Then:
auto itFound = std::find_if(cardNum, cardNum + 32, IsCharIllegal);
if(itFound != cardNum + 32)
// invalid character was entered!
There is a case to be made for using std::string instead of a raw char array too:
std::string cardNum;
cout << "Enter credit card number: ";
std::cin >> cardNum;
Followed by:
auto itFound = std::find_if(cardNum.begin(), cardNum.end(), IsCharIllegal);
if(itFound != cardNum.end())
// invalid character was entered!
That helps avoid the magic 32 and also allows inputs of any length.
I would use a regular expression to match this pattern. If you're using C++11, you can use the built in header: http://www.cplusplus.com/reference/regex/
Otherwise, take a look here for some alternative libraries you can use: C++: what regex library should I use?
Unfortunately, I'm not very good at regular expressions, but the following should match 16 numbers with spaces inbetween.
(\d[ ]*){16}
If you're looking for more info on regular expressions, here is a good cheat sheet I use often: http://regexlib.com/CheatSheet.aspx
I also like to test my expressions using this site: http://regexpal.com/
So something like this would be allowed?
"123 456 789 01 23456"
Use std::string and the free-standing std::getline function. It's better than the member function of the same name, because it doesn't force you to deal with pointers.
std::string line;
std::getline(std::cin, line);
if (!std::cin)
{
// catastrophic input failure
}
Then you have a string as in my example above in line. You could use std::find_if to verify that there are no illegal characters and std::count_if to make sure there are exactly 16 digits, but I think writing your own loop (not "bunch of loops") would yield more readable code here.
By the way, beware of isdigit! For historical reasons, you must cast its argument to unsigned char in order to use it safely.
There is an atoll function in the cstdlib. http://www.cplusplus.com/reference/cstdlib/atoll/
It converts character string input into a long long, which could store a 16 digit long credit card number, however this quits as soon as there's an non-numeric character in the input so
atoll("123456abc890")
would return 123456
If you want to check each character by character, you could just use atoi on each character then reassemble the string for each character that passes.
http://www.cplusplus.com/reference/cstdlib/atoi/