Constants in Swift

To define constants in Swift, we can use let keyword. When we define a variable using let keyword, the variable becomes immutable, meaning the value initialised can never be modified.

If we try to modify the value of a constant, Swift raises Compile time error “Cannot assign to value”.

In this tutorial, we will learn how to define a constant in Swift using let keyword.

Example

In the following program, we will define a constant PI using let keyword.

main.swift

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let PI = 3.14
print(PI)

We can use these constants in other expressions. For demonstration, let us write a program to with function that calculates the area of circle. This function makes use the PI constant we defined in the above program.

main.swift

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let PI = 3.14

func circleArea (radius: Double)-> Double {
    return PI*radius*radius
}

print("Area of cirle with radius=3 is \(circleArea(radius: 3.0))")

Output

Constants in Swift - Example

Conclusion

In this Swift Tutorial, we learned how to define a constant in Swift using let keyword.