# Expressions Expressions are a powerful way to declare relationships and connections in your user interface. They´re typically used to combine basic arithmetic with access to properties of other elements. When these properties change, the expression is automatically re-evaluated and a new value is assigned to the property the expression is associated with: ```slint,no-preview export component Example { // declare a property of type int in-out property my-property; // This accesses the property width: root.my-property * 20px; } ``` When `my-property` changes, the width changes automatically, too. Arithmetic in expression with numbers works like in most programming language with the operators `*`, `+`, `-`, `/`: ```slint,no-preview export component Example { in-out property p: 1 * 2 + 3 * 4; // same as (1 * 2) + (3 * 4) } ``` Concatenate strings with `+`. The operators `&&` and `||` express logical _and_ and _or_ between boolean values. The operators `==`, `!=`, `>`, `<`, `>=` and `<=` compare values of the same type. Access an element's properties by using its name, followed by a `.` and the property name: ```slint,no-preview export component Example { foo := Rectangle { x: 42px; } x: foo.x; } ``` The ternary operator `... ? ... : ...` is also supported, like in C or JavaScript: ```slint export component Example inherits Window { preferred-width: 100px; preferred-height: 100px; Rectangle { touch := TouchArea {} background: touch.pressed ? #111 : #eee; border-width: 5px; border-color: !touch.enabled ? #888 : touch.pressed ? #aaa : #555; } } ```