Strings and Numbers, stringstream

Text to number, number to text

#include <iostream>
#include <string>
using namespace std;

int main() {
    string a = "25";
    string b = "17";
    cout << a + b << "\n";                    // joins the text: 2517
    cout << stoi(a) + stoi(b) << "\n";        // adds the numbers: 42

    double price = stod("3.75");
    cout << price * 2 << "\n";

    string label = "Level " + to_string(5);
    cout << label << "\n";
    return 0;
}

Output

2517
42
7.5
Level 5

Splitting text into words: stringstream

A stringstream (from <sstream>) lets you use >> on a string, just like cin. It's the easy way to split a sentence into words:

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

int main() {
    string sentence = "the quick brown fox";
    stringstream ss(sentence);
    string word;
    int count = 0;
    while (ss >> word) {
        count++;
        cout << count << ": " << word << "\n";
    }
    return 0;
}

Output

1: the
2: quick
3: brown
4: fox

while (ss >> word) keeps going as long as there is another word to read.

Splitting on a comma: getline with a separator

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

int main() {
    string csv = "red,green,blue";
    stringstream ss(csv);
    string part;
    while (getline(ss, part, ',')) {
        cout << "[" << part << "]\n";
    }
    return 0;
}

Output

[red]
[green]
[blue]

Building a string

An ostringstream works like cout, but collects everything into a string:

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

int main() {
    ostringstream out;
    out << "Player " << 1 << " scored " << 3.5 << " points";
    string report = out.str();
    cout << report << " (" << report.length() << " characters)\n";
    return 0;
}

Output

Player 1 scored 3.5 points (26 characters)

Remember: Need numbers out of a line of text? Read the whole line with getline, then pull values out with a stringstream.