In this article, we are going to learn how to add parameters to a string in C# in a few different ways.
Let’s start
Using String.Format() Method
Firstly, we can add parameters to a string using the string.Format()
method. With this method, we can insert objects, variables, or expressions at specific places in a formatted string:
var name = "John Doe"; Console.WriteLine(string.Format("Hi, my name is {0}", name));
The {0}
within the format string is a format item. 0 is the index of the parameter that we insert at that position, in this case name
. However, if the value that we want to insert is not a string
, it is converted to string automatically.
Let’s add another parameter called age
which is an integer:
var name = "John Doe"; var age = 26; Console.WriteLine(string.Format("Hi, my name is {0}. I am {1} years old", name, age));
As we can see, the compiler has no problems with this and in the runtime, we get our message:
Hi, my name is John Doe. I am 26 years old.
Using String.Replace() Method
The string.Replace()
method has four overloads. But in our example, to add a parameter to a string
, we are going to use an overload that has two string parameters:
public string Replace (string oldValue, string newValue);
The oldValue
is the current string we want to replace, while newValue
is the parameter we are adding:
var greeting = "Hi, my name is username"; Console.WriteLine(greeting.Replace("username", name));
string.Replace()
method is case-sensitive. As such, if we were to pass in ‘Username’ as oldValue
in the example above, no match will be found and the current greeting
is returned.
Additionally, we can chain multiple string.Replace()
to a string
:
var age = 26; var greeting = "Hi, my name is username. I am age years old"; Console.WriteLine(greeting.Replace("username", name).Replace("age", age.ToString()));
When we run our application, both ‘username’ and ‘age’ will be replaced by name
and age
respectively. However, we had to convert age
from int
to string
as this method only accepts string variables.
This method of adding parameters to a string is not used that often.
Using String Interpolation
String interpolation is available starting with C#6. It is a more readable method for adding parameters to a string. We use $
to identify a string literal as an interpolated string, and instead of using indexes, we use the variables themselves inside braces {} which is more practical and intuitive:
Console.WriteLine($"Hi, my name is {name}. I am {age} years old");
In addition, we can use the ternary conditional operator ?: to format strings when using string interpolation:
Console.WriteLine($"Hi, my name is {name}. I am {age} year{(age == 1 ? "" : "s")} old");
As you can see, we are either returning “year” if the age is equal to 1 or “years” if it is not.
Using StringBuilder.AppendFormat()
Lastly, it’s worth mentioning that if we’re using the StringBuilder
class we can also add variables to a string by using StringBuilder.AppendFormat()
. This method exists in the System.Text
namespace. We can apply this method the same way we use string.Format()
:
var builder = new StringBuilder(); builder.AppendFormat("Hi, my name is {0}. I am {1} years old.", name, age); Console.WriteLine(builder);
The resulting string is exactly the same as before.
We also need to mention one more thing. As of .NET 6, string interpolation is more memory-efficient and faster than both String.Format
and StringBuilder.AppendFormat
. This means, we should prefer it in all cases where the format string is known at compile time.
Conclusion
In this article, we have learned how to add parameters to a string in C# using various methods and examples. We can apply this concept when building applications to send dynamic messages and feedback to users.