Converting Number to String in C++

In C++, converting integers to strings or converting numbers to strings or vice-versa is actually a big paradigm shift in itself. In general or more specifically in competitive programming there are many instances where we need to convert a number to a string or string to a number. Let’s look at some methods to convert an integer or a number to a string.

Converting Number to String in C++

There are 4 major methods to convert a number to a string, which are as follows:

• Using to_string()
• Using string Stream
• Using sprintf() function
• Using boost lexical cast

Method 1: Using to_string()

The to_string() function can be used to convert an integer, floating point values, or any number to a string. This function accepts a number(which can be any data type) and returns the number as the desired string.

Syntax:

string to_string (int val);

Parameters:

• val – Any Numerical Value.

Return Value:

• A string object containing the representation of value as a sequence of characters.

Example:

C++

// C++ code to demonstrate "to_string()" method
// to convert number to string.
#include <iostream>
#include <string> // for string and to_string()
using namespace std;

// Driver Code
int main()
{
    // Declaring integer
    int i_val = 20;

    // Declaring float
    float f_val = 30.50;

    // Conversion of int into string using
    // to_string()
    string stri = to_string(i_val);

    // Conversion of float into string using
    // to_string()
    string strf = to_string(f_val);

    // Displaying the converted strings
    cout << "The integer in string is : ";
    cout << stri << endl;
    cout << "The float in string is : ";
    cout << strf << endl;

    return 0;
}

Output

The integer in string is : 20
The float in string is : 30.500000

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 2: Using string streams

In this method, a string stream declares a stream object which first inserts a number, as a stream into an object and then uses “str()” to follow the internal conversion of a number to a string.

Example:

C++

// C++ code to demonstrate string stream method
// to convert number to string.
#include<iostream>
#include <sstream>  // for string streams
#include <string>  // for string
using namespace std;
int main()
{
    int num = 2016;

    // declaring output string stream
    ostringstream str1;

    // Sending a number as a stream into output
    // string
    str1 << num;

    // the str() converts number into string
    string geek = str1.str();

    // Displaying the string
    cout << "The newly formed string from number is : ";
    cout << geek << endl;

    return 0;
}

Output

The newly formed string from number is : 2016

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 3: Using the sprintf() function

sprintf() function stores the output on the char buffer specified in the function, instead of printing the output on the console.

C++

// C++ Program to illustrate the use of sprintf() for number
// to string conversion
#include <iostream>
using namespace std;

int main()
{
    // any num
    int n = 12234;
    // string buffer
    char str[1000];

    // sprintf() to print num to str buffer
    sprintf(str, "%d", n);

    cout << "the string is : " << str;

    return 0;
}

// this code is contributed by shivanisingh

Output

the string is : 12234

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 4: Using boost lexical cast

Similar to string conversion, the ” lexical_cast() ” function remains the same, but in the ‘boost lexical cast‘ time argument list modifies to “lexical_cast(numeric_var).  

Example:

C++

// C++ code to demonstrate "lexical_cast()" method
// to convert number to string.
#include <boost/lexical_cast.hpp> // for lexical_cast()
#include <iostream>
#include <string> // for string
using namespace std;

// Driver Code
int main()
{
    // Declaring float
    float f_val = 10.5;

    // Declaring int
    int i_val = 17;

    // lexical_cast() converts a float into string
    string strf = boost::lexical_cast<string>(f_val);

    // lexical_cast() converts a int into string
    string stri = boost::lexical_cast<string>(i_val);

    // Displaying string converted numbers
    cout << "The float value in string is : ";
    cout << strf << endl;
    cout << "The int value in string is : ";
    cout << stri << endl;

    return 0;
}

Output

The float value in string is : 10.5
The int value in string is : 17

Time Complexity: O(n)
Auxiliary Space: O(n)

This article is contributed by Manjeet Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.