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

2. Control Structures
Control structure: an instruction that determines the order in which other instructions in a program are executed
Structured programming
each logical unit of a program should have just one entry and one exit
These constructs are selection statements, looping statements, and subprogram statements
Statements are executed in sequence until an instruction is encountered that changes this sequencing

3. Sequence
Statements that are simply statements that naturally follow one another from the top of the program to the bottom

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. Selection Statements that include if statements and switch statements
Selection statements are sometimes called conditional or decision statements.
if (score >= 60) { cout << "I passed" << endl; } else { cout << "I'll do better next time!" << endl; }

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

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

11. Iteration
Statements that allow the compiler to return to a point higher in the program in order to continuously repeat one or more statements
All loops including while, do/while, and for loops are prime examples of iteration statements
while (num < 10) { cout << "hello world" << endl; num = num + 1; }

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

13. 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

14. 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.

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

16. 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.

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

18. Invocation
Statements that allow you to place a block of statements that you wish to use several times during a program in one section
You then have the ability to "call" those statements whenever you wish to execute them without having to retype the block of statements over and over again within the program
In C++, we use "function calls" as invocation statements
displayHelloWorld( ); will call (i.e. invoke) the function below
void displayHelloWorld() { cout << "hello world" << endl; }

19. Structural Review: Types of Statements
sequence
selection (if and switch structures)
iteration (for and while loops)
invocation (functions)