Converting Number to String in C++

Converting numbers to string 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. But lack of knowledge of certain essential tools binds us to do so. Some methods to achieve this task are mentioned in this article.

Converting Number to String in C++

There are 3 major methods to convert a number to a string, which are as follows:

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

Method 1: 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:   

CPP

// 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 2: Using to_string()

 The function to_string() accepts a number(which can be any data type) and returns the number in the desired string. 

CPP

// 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 3: Using boost lexical cast

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

Example:

CPP

// 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

Method: Using the sprintf() function

C++

#include <iostream>
using namespace std;

int main()
{
    int n=12234;
    char str[1000];
  sprintf(str,"%d", n);
  printf("the string is : %s",str);

    return 0;
}

Output

the string is : 12234

Time Complexity: O(n)

Auxiliary Space: O(n)

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