# String Interpolation

You are familiar with this code.

using System;

class MainClass
{
  public static void Main ()
  {
    int age = 64;
    string name = "John";
    Console.WriteLine("{0} is {1} years old", name, age);
  }
}

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Replace line 9 with this code

Console.WriteLine($"{name} is {age} years old");

Run it in your IDE. Did it work?

What is the difference between the two code?

# Explanation

The word interpolation means inserting something into something else. In Urdu it means شامل کرنا.

When a $ is placed before a string literal, it becomes an interpolated string.

In this string $"{name} is {age} years old", you can see name and age are inserted inside a string.

In simple terms, with interpolation, you can simply refer to the variables by their names.

# Expression Interpolation

Besides variables, you can also use expressions.

using System;

class MainClass
{
  public static void Main ()
  {
    string name = "John";
    int age = 40;
    int yearOfBirth = 1980;
    Console.WriteLine($"{name} is {age} years old");
    Console.Write($"In the year 2001, {name} was {2001 - yearOfBirth} years old");
  }
}

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Did you notice the {2001 - yearOfBirth}? Compiler will perform the calculation and insert the result into the string.

# Assign interpolated string to a variable

In the above examples, we have passed interpolated string to the Console.Write and Console.WriteLine methods.

You can assign interpolated string to a variable.

string result = $"In the year 2001, {name} was {2001 - yearOfBirth} years old";

← Exercise 6 Example 1 →