Is there any simple way to store an input in vector in C++ ,other then the one i have implemented below?

Question

We were given an input which we have to store in vector and do something. The input was like this

123

Now I'm currently working on it to understand the basics and working of vector like i have learned the arrays in C lang & python. Here's what I have implemented;

#include<bits/stdc++.h>
 using namespace std;

int main()
{
vector<int> v1;
  string x;
 getline(cin,x);    //takes input as string

stringstream s(x);

int temp;

for(int i=0;i<x.size();i++)
{
    char j=x[i];    //Iterating over each n every string
    int num;
    stringstream ss;
    ss<<j;
    ss>>num;     //covert the string to integer
    v1.push_back(num);
}

for(auto i=v1.begin();i!=v1.end();++i)    //output
    cout<<*i<<" ";
return 0;

}

After runnung this i will get output of vector like this:

1 2 3

Is there any easy way to implement this like in python we use .split()?

Answer 1

If it's guaranteed that the input only consists of digits only, then you can use std::cin to input, then minus each character by '0' to get the integer.

#include <iostream>
#include <vector>
#include <string>

int main()
{
    std::string inp;
    std::cin >> inp;

    std::vector<int>result;
    for (char c : inp) { result.push_back(c - '0'); }
    for (int x : result) {std::cout << x << " ";}
}

Result:

1237790
1 2 3 7 7 9 0

Else you can use std::getline (so some spaces maybe added to the input) to input, then use isdigit() to check whether a character is a digit :

#include <iostream>
#include <vector>
#include <string>

int main()
{
    std::string inp;
    std::getline(std::cin, inp);

    std::vector<int>result;
    for (char c : inp)
    {
        if (isdigit(c)) {result.push_back(c - '0');}
    }
    for (int x : result) {std::cout << x << " ";}
}

Result:

abc  123 /*78awd00
1 2 3 7 8 0 0

Some explanation :

In C++ programming language, the char data type is an integral type, meaning the underlying value is stored as an integer. More specifically, the integer stored by a char variable are interpreted as an ASCII character : ASCII table.

As you can see, digit char is represented from 48 to 57, starting from '0' and ending with '9'.

So when we take a digit char c, for example '2', and minus it by '0', we're quite literally substracting the ASCII value of '2', which is 50, to '0', which is 48, and we end up with an integer that we needed : 2.

Similar post : Convert a character digit to the corresponding integer in C

So you can see that using stringstream instead of a simple substraction is quite an overkill (but it works anyway, no objection there):

char j=x[i]; 
int num;
stringstream ss;
ss<<j;
ss>>num;

Note that using namespace std; and #include <bits/stdc++.h> is highly warned against:

• Why is "using namespace std;" considered bad practice?

• Why should I not #include <bits/stdc++.h>?

Answer 2

I didn't test it, but conceptually could look like that

#include<bits/stdc++.h>
using namespace std;

int main()
{
    string num_str; // will hold the whole number as string
    cin >> num_str;
    vector<int> digits;
    for(auto digit_ch : num_str) {
        digits.push_back(digit_ch - '0');
    }
}

The trick is in this line digits.push_back(digit_ch - '0'); where you iterate every digit as a char (like '2' or '5'), and by subtracting '0' from it, you get a numerical value of this digit (2 and 5 respectively)

Answer 3

Another option is std::for_each which can iterate over each character in inp and then with the use of a lambda, check if the character is a digit, and if so, add it to result, e.g.

    std::for_each (inp.begin(), inp.end(), [&result](int c) { 
                                            if (isdigit(c)) 
                                                result.push_back(c - '0');
                                            });

The example validating the input and using std::for_each() could be:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

int main()
{
    std::string inp;
    std::vector<int>result;
    
    if (std::getline (std::cin, inp)) {
        std::for_each (inp.begin(), inp.end(), [&result](int c) { 
                                                if (isdigit(c)) 
                                                    result.push_back(c - '0');
                                                });
    }
        
    for (int x : result) {
        std::cout << x << " ";
    }
    std::cout.put ('\n');
}

Example Use/Output

$ echo "1 2 3 4 5" | ./bin/for_each_digit
1 2 3 4 5