What's the main difference between int.Parse() and Convert.ToInt32

• If you've got a string, and you expect it to always be an integer (say, if some web service is handing you an integer in string format), you'd use Int32.Parse().

• If you're collecting input from a user, you'd generally use Int32.TryParse(), since it allows you more fine-grained control over the situation when the user enters invalid input.

• Convert.ToInt32() takes an object as its argument. (See Chris S's answer for how it works)

  Convert.ToInt32() also does not throw ArgumentNullException when its argument is null the way Int32.Parse() does. That also means that Convert.ToInt32() is probably a wee bit slower than Int32.Parse(), though in practice, unless you're doing a very large number of iterations in a loop, you'll never notice it.

Have a look in reflector:

int.Parse("32"):

public static int Parse(string s)
{
    return System.Number.ParseInt32(s, NumberStyles.Integer, NumberFormatInfo.CurrentInfo);
}

which is a call to:

internal static unsafe int ParseInt32(string s, NumberStyles style, NumberFormatInfo info)
{
    byte* stackBuffer = stackalloc byte[1 * 0x72];
    NumberBuffer number = new NumberBuffer(stackBuffer);
    int num = 0;
    StringToNumber(s, style, ref number, info, false);
    if ((style & NumberStyles.AllowHexSpecifier) != NumberStyles.None)
    {
        if (!HexNumberToInt32(ref number, ref num))
        {
            throw new OverflowException(Environment.GetResourceString("Overflow_Int32"));
        }
        return num;
    }
    if (!NumberToInt32(ref number, ref num))
    {
        throw new OverflowException(Environment.GetResourceString("Overflow_Int32"));
    }
    return num;
}

Convert.ToInt32("32"):

public static int ToInt32(string value)
{
    if (value == null)
    {
        return 0;
    }
    return int.Parse(value, CultureInfo.CurrentCulture);
}

As the first (Dave M's) comment says.

No difference as such.
Convert.ToInt32() calls int.Parse() internally

Except for one thing Convert.ToInt32() returns 0 when argument is null

Otherwise both work the same way