C++ Program For String to Long Conversion

A numeric string can be converted into an integer type when its value needs to be used in arithmetic or other numeric operations.n C++ provides stol(), stoul(), and atol() for converting strings into signed or unsigned long values.

• stol() converts a std::string to long.
• stoul() converts a std::string to unsigned long, while atol() works with C-style strings.

Examples:

Input: s1 = "20", s2 = "30"
Output: long: 50

Input: s = "123456654"
Output: 123456654

Methods to Convert String to Long

The conversion can be performed using the following methods:

1. Using stol()

The std::stol() function converts a std::string containing an integer into a long value.

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

int main()
{
    string s1 = "20";
    string s2 = "30";

    // Convert strings to long
    long n1 = stol(s1);
    long n2 = stol(s2);

    // Add the converted values
    long result = n1 + n2;

    cout << "long: " << result;

    return 0;
} 

long: 50

Explanation

• stol() converts "20" and "30" into long values.
• The converted values are added to obtain 50.

2. Using stoul()

The std::stoul() function converts a std::string into an unsigned long value. It is suitable for non-negative integer values.

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

int main()
{
    string s1 = "20";
    string s2 = "30";

    // Convert strings to unsigned long
    unsigned long n1 = stoul(s1);
    unsigned long n2 = stoul(s2);

    // Add the converted values
    unsigned long result = n1 + n2;

    cout << "unsigned long: " << result;

    return 0;
} 

unsigned long: 50

Explanation

• stoul() converts the numeric strings into unsigned long values.
• The converted values are added to obtain 50.

3. Using atol()

The atol() function converts a C-style string (const char*) containing an integer into a long value. It is available through the <cstdlib> header.

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

int main()
{
    const char* str = "123456654";

    // Convert C-style string to long
    long num = atol(str);

    cout << num;

    return 0;
} 

123456654

Explanation

• atol() accepts a C-style string.
• It converts the numeric text into a long value.
• The converted value is stored in num.