How to get a certain element from an input (C++)

Question

I am new to programming in C++. I am trying to ask the user an input (for example):

std::string numbers;
std::cout << What is your favorite number;
std::cin >> numbers

If the user entered

1, 2, 3

How do I extract only the number "2"? I know in python, you would do something like numbers[1], but is there a same way in C++ as well?

Read basic input functionality: http://www.cplusplus.com/doc/tutorial/basic_io/ — XCS, Jan 17 '14 at 22:06
@Cristy please don't suggest people to read cplusplus tutorials (And cplusplus in general), contains very bad and old practices. — Manu343726, Jan 17 '14 at 22:10
Have you tried even building your code? Cause you're missing "" in cout — prajmus, Jan 17 '14 at 22:10

score 3 · Answer 1 · edited May 23 '17 at 11:51

3

So, "what are your favorite numbers?"

The idea is the same as in python or any other language: split the input line by the separator character, trim if you care, and finally get the element you want, if it exists.

Splitting a string by a character
Eventually, trim
Finally, you should have a vector of string, and you can get the second with v[1] or similar, checking if it exists

edited May 23 '17 at 11:51

Community

1
1

answered Jan 17 '14 at 22:08

ShinTakezou

9,432
1
29
39

thestar · Accepted Answer · 2014-01-17T22:25:44.447

2

you can get the length of string by numbers.length().

then you can use for loop.

for(int i =0 ; i < numbers.length();i++)
{
  if(numbers[i] == '2')
     // do what you want you do here with 2
}

Keep in mind, your cin won't get entire "1, 2, 3" string because of whitespace. You should use getline instead of cin.

such as..

getline(cin, numbers,'\n');

edited Jan 17 '14 at 22:25

answered Jan 17 '14 at 22:10

thestar

4,959
2
28
22

score 1 · Answer 3 · answered Jan 17 '14 at 22:45

To catch a line of numbers:

int main()
{
     std::vector<int>    numbers;
     std::string line;
     std::getline(std::cin, line);           // First read the whole line of input

     std::stringstream linestream(line);     // Set up to parse the line
     int               number;
     while(linestream >> number) {           // Read a number
        char x;                              // for the comma
        linestream >> x;                     // remove the comma

        numbers.push_back(number);           // Add to the vector (array)
     }

     // Print the number
     std::cout << "The second number is: " << numbers[1] << "\n";  // vectors are 0 indexed
}

How to get a certain element from an input (C++)

3 Answers3