Difference between int.Parse , Convert.ToInt32 and int.TryParse

int.Parse(string s)

• Simply, int.Parse (string s) method converts the string to integer.
• If string s is null, then it will throw ArgumentNullException. 
• If string s is other than integer value, then it will throw FormatException.
• If string s represents out of integer ranges, then it will throw OverflowException.

Example:

1. class Program
2. {
3.         static void Main(string[] args)
4.         {
5.             string  Num1="123";
6.             string  Num2=null;
7.             string  Num3="123.6743";
8.             string  Num4="34909564545464509123409"; 
9.             int finalResult;
10.             finalResult = int.Parse(Num1); //success
11.             finalResult = int.Parse(Num2); // ArgumentNullException
12.             finalResult = int.Parse(Num3); //FormatException
13.             finalResult = int.Parse(Num4); //OverflowException 
14.         }
15.     } 

Convert.ToInt32(string s)

• Simply, Convert.ToInt32(string s) method converts the string to integer.
• If string s is null, then it will return 0 rather than throw ArgumentNullException.
• If string s is other than integer value, then it will throw FormatException. 
• If string s represents out of integer ranges, then it will throw OverflowException.

Example:

1. class Program
2.     {
3.         static void Main(string[] args)
4.         {
5.             
6.             string  Num1="123";
7.             string  Num2=null;
8.             string  Num3="123.6743";
9.             string  Num4="34909564545464509123409"; 
10.             int finalResult;
11.             finalResult = Convert.ToInt32(Num1); 
12.             finalResult = Convert.ToInt32(Num2); 
13.             finalResult = Convert.ToInt32(Num3); 
14.             finalResult = Convert.ToInt32(Num4); 
15.         }
16.     }

int.TryParse(string s,Out)

• Simply int.TryParse(string s,out int)method converts the string to integer out variable and   returns true if successfully parsed, otherwise false. 
• If string s is null, then the out variable has 0 rather than throw ArgumentNullException. 
• If string s is other than integer value, then the out variable will have 0 rather than             FormatException.
•  If string s represents out of integer ranges, then the out variable will have 0 rather than   throw OverflowException.

Example

1. class Program
2. {
3.     static void Main(string[] args)
4.     {
5.         
6.             string  Num1="123";
7.             string  Num2=null;
8.             string  Num3="123.6743";
9.             string  Num4="34909564545464509123409"; 
10.         int finalResult;
11.         bool output;
12.         output = int.TryParse(Num1, out finalResult); // 9009
13.         output = int.TryParse(Num2, out finalResult); // 0
14.         output = int.TryParse(Num3, out finalResult); // 0
15.         output = int.TryParse(Num4, out finalResult); // 0 
16.     }
17. }

What is the difference between Convert.ToInt32 and (int)?

(int)foo is simply a cast to the Int32 (int in C#) type. This is built into the CLR and requires that foo be a numeric variable (e.g. float, long, etc.) In this sense, it is very similar to a cast in C.

Convert.ToInt32 is designed to be a general conversion function. It does a good deal more than casting; namely, it can convert from any primitive type to a int (most notably, parsing a string). You can see the full list of overloads for this method here on MSDN.