1. CPS120: Introduction to Computer Science
File Processing: Basic Structure

2. File Structure

3. Basic Structure

4. Sequence Control Structures
Sequence control structures direct the order of program instructions.
The fact that one instruction follows another—in sequence—establishes the control and order of operations.

5. Calculate Add 1 to Counter
A program can instruct a computer to perform mathematical operations.
Add 1 to Counter

6. Store
A program will often instruct a computer to store intermediate results.
Place 1 in Counter

7. Compare and Branch
A program can instruct a computer to compare two items and do something based on a match or mismatch which, in turn, redirect the sequence of programming instructions.
There are two forms:
IF-THEN
IF-THEN-ELSE

8. IF-THEN
false
true
Entry
Exit
True statement a
Test condition p

9. IF-THEN-ELSE Entry Exit Test condition p “true” statement a
false
true
Entry
Exit
Test condition p
“true” statement a
“false” statement a

10. Iterate
A program loop is a form of iteration. A computer can be instructed to repeat instructions under certain conditions.

11. Iteration Control Structures
Iteration control structures are looping mechanisms.
Loops repeat an activity until stopped. The location of the stopping mechanism determines how the loop will work:
Leading decisions
Trailing decisions

12. Leading Decisions
If the stop is at the beginning of the iteration, then the control is called a leading decision.
The command DO WHILE performs the iteration and places the stop at the beginning.

13. DO WHILE Loop No
Yes
Entry
Exit
Test condition p
Loop statement a

14. Trailing Decisions
If the stop is at the end of the iteration, the control mechanism is called a trailing decision.
The command DO UNTIL performs the iteration and puts the stop at the end of the loop.

15. DO UNTIL Loop No
Yes
Entry
Test condition p
Exit
Loop statement a