✅ why are they considered int instead of string?

 CS1503: Argument 1: cannot convert from 'string' to 'int' (in Solution.cs)

public class Solution {
    public bool BackspaceCompare(string s, string t) {
        var dic1 = new Dictionary<string, string>(){
            {" ", "#"},
            {"  ", "##"},
            {"   ", "###"}
        };
        
        var dic2 = new Dictionary<string, string>(){
            {" ", "#"},
            {"  ", "##"},
            {"   ", "###"}
        };
        
        for(int i = 0; i < s.Length; i++){
            string sStr = s[i].ToString();
            string tStr = t[i].ToString();
            if(!dic1.ContainsKey(sStr)){
                dic1.Add(sStr, " ");
            }
            
            if(!dic2.ContainsKey(tStr)){
                dic2.Add(tStr, " ");
            }
        }
        
        foreach(var k in dic1.Keys){
            string sForEach = s[k].Convert.ToString(); //ERROR HERE
            string tForEach = t[k].Convert.ToString(); //ALSO HERE
            if(dic2.ContainsKey(k) && sForEach == tForEach){
                return true;
            }
        }
        
        return false;
    }
}