How can I convert a string to int? [duplicate]

The Problem is that "j" is an int, and you are assigning it to the return of GetKey. Either make "j" a string, or change the return type of GetKey to int.

Try this:

j = Int32.Parse(GetKey((keys + i).ToString())); 

It will throw an exception if the value is not a valid integer.

An alternative is the TryParse, which returns a boolean if the conversion was not successful:

j = 0; Int32.TryParse(GetKey((keys + i).ToString()), out j); // this returns false when the value is not a valid integer. 

try to improve your code, and look this:

public List<int> GetListIntKey(int keys) { var t = new List<int>(); for (int i = 0; ; i++) { var j = GetKey((keys + i).ToString()); int n; // check if it's possible to convert a number, because j is a string. if (int.TryParse(j, out n)) // if it works, add on the list t.Add(n); else //otherwise it is not a number, null, empty, etc... break; } return t.Count == 0 ? null : t; } 

I hope it help you! :)

You are getting the error because GetKey returns a string and you are trying to assign the return object to j which is declared as an int. You need to do as alfonso suggested and convert the return value to an int. You can also use:

j = Convert.ToInt32(GetKey((keys+i).ToString())); 

What should i do ? 

You have it all wrong. Read about value types and reference types.

Errors:

1. Error is Cannot implicitly convert type 'string' to 'int'. Meaning implicitly it is getting a string which it cannot convert to int. GetKeys is returning string which you are trying to assign to integer j.

2. Your j is integer. How can it be checked with null. When can a value type be null?

Use this

public List<int> GetListIntKey(int keys) { int j = 0; List<int> t = new List<int>(); for (int i = 0; ; i++) { string s = GetKey((keys + i).ToString()); if (Int.TryParse(s, out j)) break; else t.Add(j); } if (t.Count == 0) return null; else return t; } 

You have to use an exppicit type cast.

Use

int i = Convert.ToInt32(aString); 

to convert.