Cannot implicitly convert "string" to "int" when reading integers from a file

Question

I am new to C# and needing some help. If someone could explain why this is happening and not just give me an answer, that would be much appreciated.

I get the following error message:

Cannot implicitly convert string to int

Here is my code:

int[] arrayData = new int[12];

StreamReader scores = new StreamReader("scores.txt")

while (scores.Peek() != null)
{
    arrayData[counter] = scores.ReadLine();  // <-- above error occurs here
    counter = counter + 1;
}

scores.Close();

I also have one other question if someone can help.

string x = …
int y = …
if (x > y) …  // <-- below errors occurs here 

Error messages:

Operator > cannot be applied to string and int

Answer 1

The ReadLine() method returns a string and you are assigning it to an element of an int[] which is an array of int. Because it's the wrong type, the compiler checked whether there was an automatic conversion between the type you are assigning (string) and the type of the variable to which you are assigning it (int). But no implicit conversion from string to int exists, because not all strings can be converted to ints. Hence you "cannot implicitly convert string to int".

What can you do about this situation? In this case, while there is no implicit conversion, there may be an explicit conversion.

string foo = scores.ReadLine();
array[counter] = int.Parse(foo);

Of course this assumes that the line of text that you read into foo contains nothing but a number rendered as text. If there's other stuff you will need to parse the string, which is a whole lot more involved.

Your second question about the comparison is actually the same problem - when you try to compare two different types implicit conversion is attempted and fails. Then you get an error message that you can't compare them. The solution is the same: convert the string to an int using int.Parse(string) as per my example above.

You could convert the int to a string like this:

string ystring = y.ToString();

Then you could compare x with ystring because they're both strings. But this is probably a bad idea, because numbers than have been converted to strings sort differently from how they sort as numbers:

1
10
2

In Hossein's answer you may notice that he uses Convert.ToInt(string) rather than int.Parse(string). They do the same thing, but Convert is a static object exporting a wide variety of conversions. Given that you are only just now learning about type compatibility, you probably aren't ready for the complexity of Convert class. But don't let that stop you from examining it and reading all the documentation for it on http://msdn.microsoft.com because you will find it both educational and useful.

Answer 2

Short Answer:
Use either

int.Parse();
Convert.ToInt32();

methods like this :

int[] arrayData = new int[12];

StreamReader scores = new StreamReader("scores.txt")

while (scores.Peek() != null)
{
    arrayData[counter] = int.Parse(scores.ReadLine());  
    counter = counter + 1;
}

scores.Close();

You need to convert the string value to int so that you can assign it or use it in comparisons such as

if (x > y) …

Long Explanation:
The error is self explanatory, You are reading an string and are trying to assign it to a whole different type! The ReadLine() method returns a string, And string is different than int.
In C# you have different types and for each of them you must use a compatible value.
int is number (actually a number is an integer so you use int to store and work with numbers ( integer values).
string is an array of characters such as

"Ali","Alex","Apple",....

anything which is placed between a double quote is considered a string in c#.
so basically

1 doesn't equal to "1"

Although they look the same, they are completely different.(its as if you compare a picture of an apple with a real one! they look the same, but they are completely two different things!)

So if you need to extract that number out of the string, you need conversion and in that case if you want to have a conversion you can use Convert.ToInt() method you may also use :

Int32.Parse();

Have a look at here And Also a similar question here

For the same reason you can not use such operators on different types.

So to cut a long story short, you need to do this :

int[] arrayData = new int[12];

StreamReader scores = new StreamReader("scores.txt")

while (scores.Peek() != null)
{
    arrayData[counter] = int.Parse(scores.ReadLine());  
    counter = counter + 1;
}

scores.Close();

Answer 3

While a string can contain a textual representation of a valid int number (such as "1"), it is not an int (1). A string could also be something other than the textual representation of an integer number, e.g. "ABC", and it clearly wouldn't make sense to have a comparison such as "ABC" > 1, right? This is one reason why the > operator is not defined for the combination of a string and an int: it would not be guaranteed to be meaningful in all cases.

The reason why int x = Console.ReadLine(); doesn't work is the same: that method returns a string, and your variable is typed int. These types are not implicitly convertible.

Here's what you need to do: Convert the textual representation of an integer number inside the string into an int, using int.Parse or int.TryParse:

string text = Console.ReadLine(); // get user input; we cannot know whether a number
                                  // was entered or something else!

int a = int.Parse(text); // might throw an exception if `text` doesn't contain
                         // a textual representation of a valid int number
int b;
if (int.TryParse(text, out b))
{
    // contents of `text` could be converted to an `int`, which is now stored in `b`
}
else
{
    // contents of `text` could not be converted to an `int`, but no exception
    // has been thrown; instead we end up here.
}

Answer 4

The string content of the primary array must be converted to the type of the destination array, is which integer... So here it comes:

while (scores.Peek() != null)
{
    arrayData[counter] = Convert.ToInt32(score.ReadLine());
    counter = counter + 1; 
}