Extract integers from string and store in vector using C++

Reading time: 10 minutes | Coding time: 5 minutes

Introduction

In this article we will learn how to extract integers from a string and store it in a vector using C++.

First let's define vectors and strings. Vectors are more robust versions of arrays and less error-prone compared to arrays. Unlike arrays where it's static and their size is needed to be declared beforehand, vectors are dynamic and can resize itself. The benefits of using vectors is it can allocate space for growth, however, because of this they also consume more memory compared to using arrays. Strings are one-dimensional arrays that represent sequences of characters like integers and letters.

Now let's look into a sample problem:

   Input: String = "There are 5 dogs and 3 cats."
   Output: 5 3

   Input: String = " OpenGenus 11 22 234 test"
   Output: 11 22 234

To extract the integers from the string we will be using stringstream. Stringstream is a stream class in C++ that let you operate on strings. Stringstream lets you read, extract, or insert into a string object. We will pass the string to a stringstream and using a loop we can look into each word and check if it's an integer. If an integer is detected it will be appended to a vector. The loop will continue until it reached the end of the string.

Algorithm

1. Pass the string to stringstream
   
2. In a loop, go through each word
   
3. Check if the word is an integer or not
   
4. Store values in the vector
   

Complexity

• Worst case time complexity: Θ(N)
• Average case time complexity: Θ(N)
• Best case time complexity: Θ(1)

Implementations

   
    #include <iostream>
    #include <sstream>
    #include <vector>
    using namespace std;

    int main()
    {
        stringstream ss;
        string str = " OpenGenus 11 22 234 test";

        // store the string to string stream
        ss << str;

        //declare vector 
        vector< int > intValues;

        string temp;
        int number;
        while (!ss.eof()) {

            //for getting each word in the string
            ss >> temp;

            // check for integers
            if (stringstream(temp) >> number){
                // if it is an integer value will be pushed to the vector
                intValues.push_back(number); 
            }

        }
        // print values inside the vector
         for (int i=0; i<intValues.size(); i++){
            cout<<intValues[i] << " ";
         }
        return 0;
    }
    

Output:

Applications

• Can be used to get integer values from string input from users.
• Vectors can be used when the size of values to be stored is unknown.

With this article at OpenGenus, you must have the complete idea of how to Extract integers from string and store in vector using C++.