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string oldString = "1+1=";
string newString = oldString+"2"; //newString = "1+1=2"
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string s = "";
s = s + myChar.ToString(); // Where myChar is the char to be added
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string fName = "hello ";
string lName = "world";
string Name = string.Concat(fName, lName);
//or
string firstName = "hello ";
string lastName = "world";
string name = firstName + " " + lastName;