In C#, We can easily convert a string to an integer in multiple ways as mentioned below,

• Using Int32.Parse() method
• Using Int32.TryParse() method 
• Using Convert.ToInt32() method

Using Int32.Parse() method

Int32.Parse() method is used to convert a string to an integer in C#. We will use Int32 or int to parse the string.

using System;

namespace ConvertStringToInt
{
    class Program
    {
        public static void Main()
        {
            string Numstr = "75";
            // Parse() method is used to convert a string to an integer
            int num = Int32.Parse(Numstr);
            // OR
            //int num = int.Parse(Numstr);   

            Console.WriteLine(num);

            Console.ReadKey();
        }
    }
}

Output:

75

If in case of conversion failure, the Parse method will return FormatException. We will use try...catch block to handle this exception.

using System;

namespace ConvertStringToInt
{
    class Program
    {
        public static void Main()
        {
            string Numstr = "75abc";   // Invalid input 

            try
            {
                int num = Int32.Parse(Numstr);
                Console.WriteLine(num);
            }
            catch (FormatException) 
            {
                Console.WriteLine("Invalid input");
            }

            Console.ReadKey();
        }
    }
}

Output:

Invalid input

Using Int32.TryParse() method 

Int32.TryParse() method is used to convert a string into an integer. If the conversion is successful then it returns true otherwise returns false.

using System;

namespace ConvertStringToInt
{
    class Program
    {
        public static void Main()
        {
            string Numstr = "75";            

            // This method returns true if success
            bool success = Int32.TryParse(Numstr, out int num);
            // OR
            //bool success = int.TryParse(Numstr, out int num);

            if (success)            
                Console.WriteLine(num);            
            else            
                Console.WriteLine("Invalid input.");            

            Console.ReadKey();
        }
    }
}

Output:

75

Using Convert.ToInt32() method

Convert.ToInt32() method is also doing the same job as the above methods do as shown below,

using System;

namespace ConvertStringToInt
{
    class Program
    {
        public static void Main()
        {
            string NumStr = "101";

            // ToInt32 method converts a string to an integer
            int num = Convert.ToInt32(NumStr);
            Console.WriteLine(num);
            Console.ReadKey();
        }
    }
}

Output:

101

If the conversion fails, the ToInt32 method returns the FormatException. We will use try..catch block to handle the exception.