C# How to Convert String to Double with Examples

In C#, convert a string to a double using double.Parse(stringValue) or safely with double.TryParse(stringValue, out double result) to avoid errors.

Examples

Input"123.45"

Output123.45

Input"-98.76"

Output-98.76

Input"abc"

OutputConversion failed (TryParse returns false)

How to Think About It

To convert a string to a double, first consider if the string is always a valid number. If yes, use double.Parse. If not, use double.TryParse to check and convert safely without errors.

Algorithm

1

Get the input string.

2

Try to convert the string to a double using a safe method.

3

If conversion succeeds, return the double value.

4

If conversion fails, handle the error or return a default value.

Code

csharp

using System;
class Program {
    static void Main() {
        string input = "123.45";
        if (double.TryParse(input, out double result)) {
            Console.WriteLine(result);
        } else {
            Console.WriteLine("Conversion failed");
        }
    }
}

Output

123.45

Dry Run

Let's trace converting "123.45" using TryParse.

1

Input string

input = "123.45"

2

Try to convert

double.TryParse("123.45", out result) returns true, result = 123.45

3

Output result

Print 123.45

Step	Input	TryParse Result	Output
1	"123.45"	true	123.45

Why This Works

Step 1: Parsing the string

double.Parse converts a valid numeric string directly to a double but throws an error if invalid.

Step 2: Safe conversion

double.TryParse attempts conversion and returns true or false without throwing errors, making it safer.

Step 3: Using the result

If TryParse returns true, the converted double is stored in the output variable for use.

Alternative Approaches

double.Parse

csharp

using System;
class Program {
    static void Main() {
        string input = "123.45";
        double result = double.Parse(input);
        Console.WriteLine(result);
    }
}

Throws an exception if the string is not a valid number, so use only when sure input is valid.

Convert.ToDouble

csharp

using System;
class Program {
    static void Main() {
        string input = "123.45";
        double result = Convert.ToDouble(input);
        Console.WriteLine(result);
    }
}

Also converts string to double but throws exception on invalid input; similar to Parse.

Complexity: O(n) time, O(1) space

Time Complexity

Conversion scans the string once, so time depends linearly on string length.

Space Complexity

Uses constant extra space for the output double variable.

Which Approach is Fastest?

double.Parse and double.TryParse have similar speed; TryParse is safer for unknown input.

Approach	Time	Space	Best For
double.Parse	O(n)	O(1)	Known valid strings
double.TryParse	O(n)	O(1)	Unknown or user input strings
Convert.ToDouble	O(n)	O(1)	Similar to Parse, with null handling