Convert Long to String in C++

Given a long integer, the task is to convert it into its equivalent string representation in C++.

• The conversion can be performed manually by processing individual digits.
• C++ also provides stringstream and std::to_string() for simpler conversions.

Examples:

Input: N = -10243213
Output: -10243213

Input: N = 42131983
Output: 42131983

Approaches to Convert Long to String in C++

The following approaches can be used:

1. Using a Custom Conversion Function

The number can be converted digit by digit. Since digits are extracted from right to left, a stack is used to restore their original order.

Steps:

1. Handle the sign of the number.
2. Extract the last digit using % 10.
3. Convert the digit into a character by adding '0'.
4. Store the characters in a stack.
5. Pop the characters and append them to the result string.

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

// Function to convert long long to string
string longToString(long long num)
{
    // Handle zero separately
    if (num == 0)
        return "0";

    bool isNegative = num < 0;

    // Use unsigned arithmetic to safely handle LLONG_MIN
    unsigned long long value =
        isNegative ? -(unsigned long long)num
                   : (unsigned long long)num;

    stack<char> digits;

    // Extract digits from right to left
    while (value > 0) {
        digits.push('0' + value % 10);
        value /= 10;
    }

    string result;

    // Restore digits to their original order
    while (!digits.empty()) {
        result += digits.top();
        digits.pop();
    }

    // Add the negative sign if required
    if (isNegative)
        result = "-" + result;

    return result;
}

int main()
{
    long long num = -10243213;

    cout << longToString(num);

    return 0;
} 

-10243213

Explanation: For num = -10243213:

• The negative sign is handled separately, and the digits are extracted from right to left using % 10.
• The digits are converted to characters, stored in a stack, and then popped to restore their original order before adding the negative sign.

2. Using stringstream

The stringstream class from the <sstream> header can convert a numeric value into a string by inserting the value into the stream and retrieving the resulting string using str().

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

int main()
{
    long long num = 43543422;

    stringstream stream;

    // Insert the number into the stream
    stream << num;

    // Convert stream contents to a string
    string result = stream.str();

    cout << result;

    return 0;
} 

43543422

Explanation

• A stringstream object is created.
• The long integer is inserted into the stream using <<.
• The str() function retrieves the stream contents as a string.
• The resulting string is printed.

3. Using std::to_string()

C++11 introduced std::to_string(), which provides a simple way to convert numeric values into strings.

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

int main()
{
    long long num = 76456474;

    // Convert the number to a string
    string result = to_string(num);

    cout << result;

    return 0;
} 

76456474

Explanation

• std::to_string() directly converts the numeric value into its string representation.
• It also handles negative values automatically.