Program may be executed from start to finish via a single function call, or step by step.
When executing programs step by step each next instruction execution takes one function call. Such, the application initializes program execution and than for as long as the program execution hasn't completed and application so desires, it executes the program instructions.
By and large, each coded expression translates to an executable instruction and control statements add each one or two extra executable instructions.
Before step by step execution programs need undergo some step by step execution required transform.
The step by step program execution also requires some step by step execution context created before execution commences. Applications will like to dispose of such context once program execution completed.