C++ Convert Int to String

In fact, the conversion of numbers to strings or vice versa represents a significant paradigm change. We often need to convert a number to a string or a string to a number in general, or more especially in competitive programming. But we can't do so fluently because we have inadequate knowledge of some crucial skills. In this article, a few approaches to doing this work are discussed.

Number to String Conversion in C++:

The three main ways to change a number into a string are as follows:

• By using string Stream 
• By using to_string()
• By using boost lexical cast

First approach: String Streams:

In this method, a stream object is declared that first inserts a number as a stream into an object before using "str()" to carry out the internal conversion of a number to a string.

C++ Program:

#include<iostream> //header files
#include <sstream> 
#include <string>


using namespace std;
int main()
{
	//initializing an integer
	int value = 2001;


	ostringstream strng1;


	strng1 << value;


	// changing number into string
	string s1 = strng1.str();


	//printing the string
	cout << " The freshly created number string is: ";
	cout << s1 << endl;


	return 0;
}

Output:

The freshly created number string is: 2001

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

Second approach: to_string():

The to_string() method takes a number, which can be of any data type, and returns it as the specified string.

C++ Program:

#include <iostream> //header files
#include <string>


using namespace std;




int main()
{
	//initializing an integer number
	int inval = 25;
	
	//initializing a floating number
	float flval = 15.03;


	//changing int to string
	string strng_i= to_string (inval);


	// changing float to string
	string strng_f = to_string (flval);


	// printing the converted strings
	cout << "In string, the integer is: ";
	cout << strng_i << endl;
	cout << "In string, the float is: ";
	cout << strng_f << endl;


	return 0;
}

Output:

In string, the integer is: 25
In string, the float is: 15.030000

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

Third approach:  Boost Lexical Cast:

Similar to how string conversion works, the "lexical cast()" method stays the same, but the argument list changes when using "boost lexical cast," becoming "lexical_cast(num_var)".

C++ Program:

#include <boost/lexical_cast.hpp> //header files
#include <iostream>
#include <string> 
using namespace std;




int main()
{
	//initializing a floating number
	float fl_val = 17.6;


	//initializing an integer number
	int in_val = 21;


	// changing float to string
	string strng_f = boost::lexical_cast<string>(fl_val);


	//changing int to string
	string strng_i = boost::lexical_cast<string>(in_val);


	// printing the converted strings
	cout << "In string, the float is: ";
	cout << strng_f << endl;
	cout << "In string, the integer is: ";
	cout << strng_i << endl;


	return 0;
}

Output:

In string, the float is: 17.6
In string, the integer is: 21

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