Accessing cloud computing resources via an API is one of the most important features that distinguish it from traditional hosting. Using an API means you are able to create and delete instances at will without the intervention of an operator. This way, it becomes very easy to implement features such as load-based autoscaling, advanced deployments (Canary releases or Blue-Green), and automated development and testing environments for an application.
Cloud providers usually expose their APIs as RESTful services. On top of that, they often also provide client libraries for several programming languages. While all of the three most popular providers support C++ as a client library, the support from smaller vendors may vary.
If you're thinking about deploying your C++ application to the cloud and plan on using the Cloud API, make sure your provider has released a C++ Software Development Kit (SDK). It is still possible to use the Cloud API without an official SDK...