Control Structure
A control structure is a programming construct that allows programmers to control the flow of execution of a program. Control structures are used to make decisions, repeat loops, and jump to different parts of the program.
Analogy
Imagine you are driving a car. You can control the direction and speed of the car by using the steering wheel, gas pedal, and brake pedal. These controls are analogous to control structures in programming.
Examples
Some common examples of control structures include:
- If statements: If statements allow programmers to make decisions based on a condition. For example, an if statement could be used to decide whether or not to display a message to the user.
- Loops: Loops allow programmers to repeat a block of code multiple times. For example, a loop could be used to print all of the numbers from 1 to 10 to the console.
- Jumps: Jumps allow programmers to jump to a different part of the program. For example, a jump could be used to jump to the end of a loop if a certain condition is met.
Importance of Control Structures
Control structures are essential for programming. They allow programmers to write complex and powerful programs. Without control structures, programs would be very limited in what they could do.
Structure Theorem
The Structure Theorem is a theorem in theoretical computer science that states that any program can be written using only three control structures: sequence, selection, and repetition.
Explanation for Junior High School Students
Imagine you are building a LEGO house. You can build the house by following a set of instructions. The instructions tell you what steps to take in order to build the house.
Control structures in programming are similar to LEGO building instructions. They tell the program what steps to take in order to complete a task.
The Structure Theorem states that any program can be built using only three control structures: sequence, selection, and repetition.
- Sequence: Sequence means that the steps of the program are executed in order. For example, if you are building a LEGO house, you might first build the foundation, then the walls, then the roof.
- Selection: Selection means that the program chooses which step to execute based on a condition. For example, if you are building a LEGO house, you might choose to build a red roof or a blue roof.
- Repetition: Repetition means that the program repeats a step multiple times. For example, if you are building a LEGO house, you might need to repeat the step of building a wall multiple times.
Example
Here is an example of how the three control structures can be used to write a simple program:
// Sequence
if (age >= 18) {
// Selection
vote();
} else {
// Selection
waitUntilYouAreEighteen();
}
This program first checks if the user is 18 years old or older. If the user is 18 years old or older, the program calls the vote() function. Otherwise, the program calls the waitUntilYouAreEighteen() function.
The vote() function and the waitUntilYouAreEighteen() function could be more complex programs, but they would still be built using the three control structures of sequence, selection, and repetition.
Conclusion
Control structures are an essential part of programming. They allow programmers to write complex and powerful programs. The Structure Theorem states that any program can be written using only three control structures: sequence, selection, and repetition.
