Mistakes happen. Computers crash. iPhones fall out of windows of moving cars. The result may be that you accidentally lose an app, could be a favorite game that you purchased or your online banking app.
In any case, if you lose one app or all of them, the App Store knows what apps you already bought and lets you download them again (if they're still available from the App Store), free of charge. Here's how to do it on your iPhone:
Tap App Store on the Home screen.
Tap the Updates button at the bottom right of the screen.
Tap Purchased at the top of the screen.
A list of apps you purchased appears.
Tap All to see all apps you purchased or Tap Not on This iPhone to see apps you purchased that aren't on this iPhone.
There are three buttons you might see:
Open which opens the app
Update which means an update is available for the app
iCloud icon which means that you previously purchased the app but it isn't on your iPhone
Tap the iCloud icon next to the app you want to reinstall.
The button changes to a circle while the app is downloading and reads Open when the installation is complete. The app button appears on the Home screen.
When you reinstall an app, you automatically install the latest version even if you originally installed a prior version.
On iTunes, the procedure is similar:
Open iTunes on your computer and click iTunes Store.
Sign in to your account if you aren't already signed in.
Click Purchased in the Quick Links list.
Click the Apps tab and then click the iPhone tab.
Click Not on This Computer to see which apps are missing.
Click the iCloud button to download the app to your computer.
The app is downloaded to iTunes and automatically downloaded to your iPhone too, if you have activated Automatic Downloads in iTunes preferences; otherwise, sync your iPhone with iTunes and the apps will be added to your iPhone.