Convert Long to String in C++

Given a Long number N, the task is to convert the N to a string using C++.

Explanation:

Input: N = -10243213 // long input
Output: -10243213 // string output
Explanation: -10243213 is the string in the output.

Input: N = 42131983 
Output: 42131983

Approach A

In this approach, we are converting every digit of the long to the char and appending it to the resultant string.

Follow the steps below to solve the problem:  

1. If a long number is negative, store the negative sign to any variable and make the long number positive.

if (long_num < 0) {
        signValue = "-";
        long_num = -long_num; //converting number to positive value
}

2. Extract every digit from the long number one by one from the last and convert it to the character and push it to the stack.

while (long_num > 0) {

     //add last digit to stack after converting it to char    
     stringStack.push(long_num % 10 + '0');  
     long_num /= 10; // remove last digit
}

3. While the stack becomes empty, pop one by one character from the string and append it to the resultant string.

while (!stringStack.empty()) {

    // append top char of stack to string
    long_to_string += stringStack.top(); 
    stringStack.pop(); // pop char from the stack
}

4. Return the resultant string with the signValue.

return signValue + long_to_string;

Example:

C++

// C++ program to demonstrate
// long to string conversion
// digit by digit
#include <bits/stdc++.h>

using namespace std;
string LongToString(long long_num)
{
    stack<char> stringStack;
    string signValue = "";

    // if long number is negative store the negative sign to
    // the signValue variable
    if (long_num < 0) {
        signValue = "-";
        long_num = -long_num;
    }

    // while number is greate than 0, get last digit from it
    // and convert it to character by adding '0' to it, and
    // push to the stack.
    while (long_num > 0) {
        char convertedDigit = long_num % 10 + '0';
        stringStack.push(convertedDigit);
        long_num /= 10;
    }

    string long_to_string = "";

    // while stack is not empty pop the character one by one
    // and append to the resultant string.
    while (!stringStack.empty()) {
        long_to_string += stringStack.top();
        stringStack.pop();
    }

    // return the resulatant string value by appending
    // singValue to it.
    return signValue + long_to_string;
}

int main()
{
    long long_num = -10243213;
    string long_to_string = LongToString(long_num);
    cout << long_to_string;
    return 0;
}

Output

-10243213

Time Complexity & Space Complexity: O (Digit_count_of_long_number) 

Approach B

C++ contains the stringstream class inside the <stream> library. We can create an object of the stringstream class and insert the variable of any data type. It returns the string object.

• Create the object of stringstream class i.e. Stringstream stream;
• Add long number to stream object i.e. stream << 43543422;
• Get the string object from stream object using str() method i.e. long_to_string = stream.str();

Example:

C++

// C++ program to demonstrate
// long to string conversion
// using stringstream
#include <iostream>
#include <sstream>
#include <string>

using namespace std;
int main()
{
    // initialize the long number
    long long_num = 43543422;

    // create a new object of stringstream class
    stringstream stream;

    // add long number to variable of type stringstream
    stream << long_num;
    string long_to_string;

    // get string object from stringstream variable using
    // str() method
    long_to_string = stream.str();
    cout << long_to_string;
    return 0;
}

Output

43543422

Approach C

The c++ <string> library provides the std::to_string() method to convert the any datatype to the string.

String long_to_string = to_string(76456474);

Example:

C++

// C++ program to demonstrate
// long to string conversion
// using std::to_string methods
#include <iostream>
#include <string>

using namespace std;
int main()
{
    // initialize the long number
    long long_num = 76456474;
    string long_to_string;

    // convert long to string using to_string() method
    long_to_string = to_string(long_num);
    cout << long_to_string;
    return 0;
}

Output

76456474