var pw = (firstName: "Phillis", lastName: "Wheatley", born: 1753, published: 1773);

//составное форматирование:
string s = string.Format("{0} {1} was an African American poet born in {2}.", pw.firstName, pw.lastName, pw.born);

//"интерполяция" строк
string s = $"{pw.firstName} {pw.lastName} was an African American poet born in {pw.born}."

//всё это вместо старинного
string s = pw.firstName +" " +pw.lastName + " was an African American poet born in " + pw.born.ToString() +"."

string json = @"{""perPageCount"":100, ""page"":2}"

string json = $@"{""perPageCount"":{count}, ""page"":{pageN}}"
string json = @$"{""perPageCount"":{count}, ""page"":{pageN}}"

string json = $"{\"perPageCount\":{count}, \"page\":{pageN}}"

string json = $"\{\"perPageCount\":{count}, \"page\":{pageN}\}"

string json = $"\U0001F47D\"perPageCount\":{count}, \"page\":{pageN}\\U0001F47E"

string json = @"{""perPageCount"":" + count.ToString() + @"""page"":" + pageN.ToString() + "}"