How to convert string to int in C#
In C#, you can convert a string to an integer using int.Parse(), int.TryParse(), or Convert.ToInt32(). For user input or data you do not fully control, use int.TryParse() first. Reserve Parse() for trusted input and Convert.ToInt32() when you want null-safe behavior that returns 0 for null.
Quick decision guide
| Method | Use when | Behavior on invalid input |
|---|---|---|
int.TryParse() | User input, external data, or anything that might be invalid | Returns false and leaves the output variable unchanged |
int.Parse() | You know the input is valid | Throws FormatException or OverflowException |
Convert.ToInt32() | You want a null-friendly conversion path | Throws on invalid text, but returns 0 for null |
using System;
// Method 1: int.Parse() - throws exception if invalid
string validNumber = "123";
int number1 = int.Parse(validNumber);
Console.WriteLine($"Parsed: {number1}");
// Method 2: int.TryParse() - safe, no exceptions
string userInput = "456";
if (int.TryParse(userInput, out int number2))
{
Console.WriteLine($"TryParse succeeded: {number2}");
}
else
{
Console.WriteLine("TryParse failed");
}
// Method 3: Convert.ToInt32() - handles null
string nullableString = "789";
int number3 = Convert.ToInt32(nullableString);
Console.WriteLine($"Convert: {number3}");
// Handling invalid input with TryParse
string invalidInput = "abc";
if (int.TryParse(invalidInput, out int result))
{
Console.WriteLine($"Converted: {result}");
}
else
{
Console.WriteLine($"Cannot convert '{invalidInput}' to int");
}
// Default value pattern
string maybeNumber = "not a number";
int finalNumber = int.TryParse(maybeNumber, out int parsed) ? parsed : 0;
Console.WriteLine($"Final number (with default): {finalNumber}");Method Comparison
| Method | Null input | Invalid input | Empty string | Overflow |
|---|---|---|---|---|
int.Parse() | ArgumentNullException | FormatException | FormatException | OverflowException |
int.TryParse() | Returns false | Returns false | Returns false | Returns false |
Convert.ToInt32() | Returns 0 | FormatException | FormatException | OverflowException |
Use int.TryParse() for any user input or data you do not fully control.
Handling Edge Cases
// Null — TryParse and Convert handle it differently
string? nullInput = null;
Console.WriteLine(int.TryParse(nullInput, out _)); // False (safe)
Console.WriteLine(Convert.ToInt32(nullInput)); // 0 (safe)
// int.Parse(nullInput); // ArgumentNullException!
// Empty string
string empty = "";
Console.WriteLine(int.TryParse(empty, out _)); // False (safe)
// int.Parse(empty); // FormatException!
// Overflow — number outside int range (-2,147,483,648 to 2,147,483,647)
string tooBig = "99999999999";
Console.WriteLine(int.TryParse(tooBig, out _)); // False (safe)
// int.Parse(tooBig); // OverflowException!
// Whitespace — TryParse trims leading/trailing whitespace
Console.WriteLine(int.TryParse(" 42 ", out int ws)); // True, ws = 42Converting to Other Numeric Types
The same Parse / TryParse / Convert pattern works for all numeric types.
// long — for numbers larger than int.MaxValue (2,147,483,647)
long big = long.Parse("123456789012345");
// double — for decimals
double d = double.Parse("3.14");
bool ok = double.TryParse("3.14", out double dResult);
// decimal — for financial values (higher precision than double)
decimal price = decimal.Parse("19.99");
// float
float f = float.Parse("3.14");
// Convert.ToX mirrors Convert.ToInt32 behaviour (null → 0, invalid → exception)
long l2 = Convert.ToInt64("123456789012345");FAQ
Which option should I choose for user input?
Use int.TryParse() so you can show a friendly error message instead of crashing with an exception.
What about whitespace or minus signs?
TryParse() accepts leading and trailing whitespace and handles negative values correctly when the string is valid.
Why does culture matter?
Some cultures use , as the decimal separator, so culture-aware parsing matters more for double, decimal, or float than for plain integer input.
Culture-Aware Parsing
The decimal separator differs by locale (. in en-US, , in de-DE). Use CultureInfo when parsing numbers from external sources.
using System.Globalization;
// German format: . = thousands separator, , = decimal point
string german = "1.234,56";
decimal amount = decimal.Parse(german, new CultureInfo("de-DE"));
Console.WriteLine(amount); // 1234.56
// Always use InvariantCulture for machine-generated data
string invariant = "1234.56";
decimal inv = decimal.Parse(invariant, CultureInfo.InvariantCulture);
Console.WriteLine(inv); // 1234.56
// NumberStyles for additional control
string hex = "1F4";
int hexValue = int.Parse(hex, NumberStyles.HexNumber);
Console.WriteLine(hexValue); // 500
string withThousands = "1,234";
int formatted = int.Parse(withThousands,
NumberStyles.Integer | NumberStyles.AllowThousands,
CultureInfo.InvariantCulture);
Console.WriteLine(formatted); // 1234Take It Further
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