Instructions in a program arranged in a prescribed order to solve a problem. Give a requirement to several programmers, each is likely to create different program logic. As long as the program works, it may not matter. What will matter is the clarity of the logic when someone else has to modify the code later on.
Program logic is the implementation of the program's requirements and design. If the design of the application is bad, the program logic can nevertheless be professionally implemented. For example, if the user interface is poorly conceived, the program logic can execute that second-rate interface very efficiently.
Calculate, Compare and Copy
Programmers write programs that calculate, compare and copy the data brought into RAM. Decision making is accomplished with the compare and branch instructions (if this, go there). In a high-level language, the IF-THEN-ELSE statement is used. See computer
Program logic zigs and zags all over the place, and the Go To instruction causes the computer to jump to a different part of the program in RAM. Repetition is common in program logic; for example, keep scanning the input until you find "xyz." In high-level languages, DO LOOPS and FOR LOOPS accomplish this repetition. See loop
User applications are interactive and "event-driven," whereby a mouse click or screen tap is an event communicated to the application to take appropriate action.
Behind-the-scenes business applications process a group of transactions all at once at the end of some period. They are not interactive and only require the operator to start the program. The application calls the OS to perform all input and output.