C# - Exception while trying to print the last element in an array

Question

I'm getting below exception while trying to print the last element in an array.

here is my code:

int[] nums = { 1, 2, 5, 7, 8 };

Console.WriteLine("first element is " + nums[0]);
int fe = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Last element is {0}" , nums[nums.Length - 1]);
int le = Convert.ToInt32(Console.ReadLine());

Exception:

first element is 1

Unhandled Exception: System.FormatException: Input string was not in a correct format. at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) at System.Convert.ToInt32(String value) at W2Resource.BasicExProb51.Main() in C:\Users\SudhaPraveen\Documents\Visual Studio 2017\Projects\CSharpPractice21DaysPlan\W2Resource\BasicExProb51.cs:line 16 Press any key to continue . . .

Hint: the exception is not happening when you think it does. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Dec 31, 2018 at 16:28
Look at your stacktrace, you find the method which caused the exception there, it starts with at.... Compare with the methods that you use and then you know that Convert.ToInt32 threw that exception. Why? Because what was in the console was not a valid integer — Tim Schmelter
– Tim Schmelter, Commented Dec 31, 2018 at 16:29
Console.ReadLine() is not an integer which is why it is throwing an exception — koolkoda
– koolkoda, Commented Dec 31, 2018 at 16:40

AFract · Accepted Answer · 2018-12-31 16:49:12Z

Your lines :

Console.WriteLine("first element is " + nums[0]);
Console.WriteLine("Last element is {0}" , nums[nums.Length - 1]);

Are both correct.

Your exception comes from user input in

Convert.ToInt32(Console.ReadLine());

As long as your user type a value that can be parsed as an integer, it works. Else it will raise the kind of exception you have seen.

If you don't use the input value, you could just replace it by :

Console.ReadKey();

It will make the program to "pause" until the user press a random key of the keyboard.

Else, if you need to use it, you have to validate the input before to use it. For example, I suggest you to check the behavior and usage of the int.TryParse() method.

Here's one answer to a question similar to yours : https://stackoverflow.com/a/45259920/461444 But it uses int.Parse() instead of int.TryParse() as suggested, which is not as good because it requires more code and raise a useless and perfectly avoidable exception.

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