(as taken from .NET Spider)
Int32.parse(string)
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Int32.Parse (string s) method converts the string representation of a number to its 32-bit signed integer equivalent.
When s is null reference, it will throw ArgumentNullException.
If s is other than integer value, it will throw FormatException.
When s represents a number less than MinValue or greater than MaxValue, it will throw OverflowException.
Convert.ToInt32(string)
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Convert.ToInt32(string s) method converts the specified the string representation of 32-bit signed integer equivalent. This calls in turn Int32.Parse () method.
When s is null reference, it will return 0 rather than throw ArgumentNullException
If s is other than integer value, it will throw FormatException.
When s represents a number less than MinValue or greater than MaxValue, it will throw OverflowException
Int32.TryParse(string, out int)
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Int32.Parse(string, out int) method converts the specified the string representation of 32-bit signed integer equivalent to out variable, and returns true if it parsed successfully, false otherwise. This method is available in C# 2.0
When s is null reference, it will return 0 rather than throw ArgumentNullException.
If s is other than integer value, the out variable will have 0 rather than FormatException.
When s represents a number less than MinValue or greater than MaxValue, the out variable will have 0 rather than OverflowException.
Convert.ToInt32 is better than Int32.Parse, since it return 0 rather than exception. But, again according to the requirement this can be used. TryParse will be best since it handles exception itself always.