Contract Functions

Sure all these type declarations are cool, but how do we do anything with them? I am glad you asked, this is where functions come into play!

A function is a group of reusable code which can be called anywhere in your program.

Let's start to craft our vending function which will in essence be the way we use to purchase goods from the vending machine!

We first start by declaring a function with the function keyword which is…that’s right you guessed it function. Then as with all types we need to give it a name, like buyItem. We also need to tell it which item we want to buy!

This is where our array indexing comes in handy!

We know that we stored all of our items in a struct array, so now all we have to do is call that item where it is stored sequentially in our array and this will be sure as our make-shift vending machine code system. In real life we would press A1 or C3 to pick our item, here it would be element 0, 1, 2, etc.

So we now know we need a function that takes a single parameter, which is a numbered index of our struct array. We can call this parameter itemCode and declare it an integer.

function buyItem (uint itemCode) public {

}

We know vending machines only dispense one item at a time so we can easily now subtract 1 from the quantity from the item we chose.

We can subtract it directly from it in our array.

allItems[itemCode].quantity -= 1;

We reference our array and reference the element with our parameter (itemCode) followed by .quantity to reference the quantity portion of our struct and then subtract one with -= 1.

So right now our function is to purchase items from our vending machine and take it out of the inventory.