C++ Program For String to Double Conversion

A string can be converted to a floating-point value when numerical calculations are required on textual data. C++ provides functions such as stod(), stold(), and atof() for converting numeric strings into floating-point values.

• stod() converts a string to double.
• stold() converts a string to long double, while atof() converts a C-style string to double.

Examples:

Input: "14.25"
Output: 14.25

Input: "34.87"
Output: 34.87

Methods to Convert String to Double in C++

The conversion can be performed using the following methods:

1. Using stod()

The stod() function converts a std::string containing a valid floating-point number into a double.

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

int main()
{
    string str = "14.25";

    // Convert string to double
    double num = stod(str);

    cout << num;

    return 0;
} 

14.25

Example: For the input string "14.25":

• stod() reads the numeric characters from the string.
• It converts the value to double.
• The converted value is stored in num.

2. Using stold()

The stold() function converts a std::string into a long double. It is useful when higher floating-point precision is required.

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

int main()
{
    string str = "34.87";

    // Convert string to long double
    long double num = stold(str);

    cout << num;

    return 0;
} 

34.87

Example: For the input string "34.87":

• stold() converts the string into a long double.
• The converted value is stored in num.
• The value can then be used in floating-point calculations.

3. Using atof()

The atof() function converts a C-style string (const char*) containing a floating-point number into a double. It is declared in the <cstdlib> header.

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

int main()
{
    const char* str = "14.25";

    // Convert C-style string to double
    double num = atof(str);

    cout << num;

    return 0;
} 

14.25

Example: For the input "14.25":

• atof() takes a C-style string.
• It converts the numeric text into a double.
• The converted value is stored in num.