Casting in C#

Amit Maheshwari

Hi friends,

I want to know that, In which scenario, I should be using (int), Int32.Parse and Convert.ToInt32? are they same or not? I do notice in certain condition that i cannot cast directly using (int) and I have to use Convert.ToInt32.
I am not that sure why i do that. Further I just need some confirmations from you all.

Thank you.

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
You should use a cast, (int), if :

1. You want to convert another numeric type to 'int' but there's no implicit conversion from that type to int. This generally means that the type could contain values which int does not contain and so the conversion may therefore fail or lose accuracy.

2. You have an object reference which contains a boxed int and you want to unbox it. When you assign an 'int' to an object variable, a wrapper is created on the heap and the int is copied into it - a process known as 'boxing'. To unbox it, you need to cast back to int.

For example;

double d = 3.8;
int i = (int)d; // rounds down, so loses accuracy
Console.WriteLine(i); // 3

object o = 4; // boxes the int value '4' on the heap
int j = (int)o; // unboxes it by copying it to the variable 'j'
Console.WriteLine(j); // 4
Sam Hobbs14y ago
It is true that if a null string is passed to Convert then it will not throw an exception but if an invalid string is passed to Convert then it will throw an exception.
Sam Hobbs14y ago
You need to convert the data when it is a string and you need the number so you can do calculations with it. A string and a number look totally different to the computer. It is very easy to look at the declaration of an object; if it is a string and you need to do calculations, then you must convert; casting is not enough.

Usually it is better to use the Int32.TryParse Method, so that if the text is not a valid number your program will not crash.
Satyapriya Nayak14y ago
Hi Amit,

The Convert.ToInt32(String, IFormatProvider) underneath calls the Int32.Parse. So the only difference is that if a null string is passed to Convert it returns 0, whereas Int32.Parse throws an ArgumentNullException.

Refer
http://www.codeproject.com/KB/cs/AgileWare_Convert_Int32.aspx

Thanks