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Short answer: writing step-by-step instructions for a robot exposes every assumption you forgot you were making. Blessed Emmanuel John chidera’s DEV Community article, posted September 19, 2026, uses that gap as a teaching device. It starts with a cheese sandwich, moves through entities, operations, and changing state, and ends at a C# class with properties, methods, and a constructor. This guide follows that same route, explains each step for someone new to C#, and marks where the exercise stops.
Start with instructions a robot can actually follow
The exercise opens with a direct challenge: “Write an algorithm that gives step-by-step instructions to assemble a cheese sandwich.” The imagined robot has bread, butter, a knife, a plate, and cheese, and nothing else to go on.
The author’s first attempt names the objects and then writes vague directions such as “take,” before combining ingredients with plus signs. The weakness is useful to study. A robot cannot safely infer which bread to take, how the butter should reach the bread, whether the knife is used at all, or what order the cheese goes on. The word “take” hides every physical detail that a person would fill in without noticing. A list of ingredients joined by plus signs names what goes into the sandwich but not how or where it is placed.
Where human assumptions hide
A person reading “make a cheese sandwich” silently supplies answers to questions the first draft leaves open. Writing the steps for a machine forces those answers into the open:
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- Which bread? A slice from the loaf, a slice already on the plate, or both slices of a finished sandwich?
- How is the butter moved? Is it scooped from a tub, and with what tool?
- What happens to each tool? Does the knife stay in the butter, or is it reused for the cheese?
- In what order? Does the butter go on before the cheese, and does the cheese sit on the bread or on the butter?
- Where does the result end up? On the plate, in a box, or left on the counter?
Each question is a decision the program author has to make explicitly. Programming languages are no different: a computer runs what you wrote, not what you meant.
Name the things, then name the actions
The revised model sorts the nouns by the role each one plays. The article’s categories are the useful part for beginners, because the same distinction shows up later as properties and method parameters.
| Role in the model | Item | Why the role matters |
|---|---|---|
| Entities | Bread, butter, cheese | These are the things whose condition the steps change. |
| Tool | Knife | Used by an action; it is not part of the finished sandwich. |
| Container | Plate | Where the assembly happens. It is context for the entities, separate from them. |
Operations make each step explicit
The article defines named operations, SCOOP, SPREAD, and LAY, so each step says what is done and to what. One way to write the sandwich in those terms looks like this:
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- LAY the cheese onto the buttered bread on the plate.
This is an illustration of how explicit steps read, not a complete robotics specification. It still answers the questions from the previous section: the inputs are named, the order is fixed, and the result is placed on a specific container.
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State: the same bread, a different condition
The next idea is state. Plain bread and buttered bread are the same slice of bread after a SPREAD operation. The object persists, but its condition changes. In programming terms, that condition is its state: the set of facts that describe the object at a given moment.
Operations come in two kinds. Some change state, such as SPREAD changing plain bread into buttered bread. Others only inspect it, reading the current condition and leaving it alone. The rest of the exercise depends on keeping those two kinds separate.
Commands and queries: change the state, or ask about it
The article illustrates this with a bank account. It starts with a balance of $5,000, deposits $1,000, withdraws $500, and then checks the balance.
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| Step | Operation | Kind | Balance afterward |
|---|---|---|---|
| 0 | Account opens | Starting value | $5,000 |
| 1 | Deposit $1,000 | Command (changes the balance) | $6,000 |
| 2 | Withdraw $500 | Command (changes the balance) | $5,500 |
| 3 | Check balance | Query (reads the balance) | $5,500, unchanged |
The author’s walkthrough reports $4,500 at the check. That figure equals the $5,000 start less the $500 withdrawal, so the deposit appears to have been left out of the reported result. The table uses the figure the arithmetic gives when all three operations are applied. The distinction the example makes does not depend on the exact number.
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The article calls this Command-Query Separation. Deposit and withdraw are commands: they change the account and do not return a balance. Check is a query: it returns the balance and leaves the account as it was. The term is established in software design, and the article uses it for this distinction. The example illustrates the idea; it does not establish a universal rule that every query in every language is free of side effects.
Scaling up: one template, many cars
A single bank account is easy to track in your head. The article then asks how to represent 100 cars, each with its own speed, fuel level, and engine state, without rewriting the same behavior for every car. The answer is a shared template. The template is the class; each individual car is an instance of it, carrying its own values.
Microsoft Learn’s C# documentation describes the same relationship: “In C#, the definition of a type—a class, struct, or record—is like a blueprint that specifies what the type can do.” The class tutorial on Microsoft Learn adds that a class is a type representing an entity, with operations implemented through methods and properties, and that constructors initialize new objects. See the Classes and objects tutorial – C# for the full treatment.
The blueprint analogy is an entry point, not a rule that every noun in a program must become a class. It helps you see why one definition can serve many objects, and it is enough to start the next section.
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Mapping the model onto C#
The article connects each idea from the sandwich and car examples to a C# construct. The table below restates that mapping with the car as the running case.
| Model idea | C# construct | Car example |
|---|---|---|
| Car template | Class | class Car |
| Individual car with its own values | Instance (object) | new Car(40.0) |
| Speed and fuel | Properties | Speed, Fuel |
| Engine running or not | Property | IsEngineRunning |
| Changing state through behavior | Methods | StartEngine(), Accelerate(int) |
| Reading the speed | Method (query) | CheckSpeed() |
| Setting starting values | Constructor | Car(double fuel) |
The article’s sample covers acceleration but not braking, so brake is not shown in the code below.
public class Car
{
public int Speed { get; private set; }
public double Fuel { get; private set; }
public bool IsEngineRunning { get; private set; }
public Car(double fuel)
{
Speed = 0;
Fuel = fuel;
IsEngineRunning = false;
}
public void StartEngine()
{
IsEngineRunning = true;
}
public void Accelerate(int amount)
{
if (!IsEngineRunning)
{
return;
}
Speed += amount;
}
public int CheckSpeed()
{
return Speed;
}
}
// Usage
var car = new Car(40.0);
car.Accelerate(20); // ignored: the engine is off
car.StartEngine();
car.Accelerate(20); // Speed is now 20
int current = car.CheckSpeed();Three things in this sample line up with the earlier ideas:
- The constructor sets the starting state, so every new car begins with speed 0 and the engine off.
StartEnginechanges the engine state, which is a command.Acceleraterefuses to change speed while the engine is off. That guard is a rule that prevents an invalid state.CheckSpeedonly returns a value, which is a query.
The sample is illustrative. It has not been tested or hardened for production use. It stores fuel but does not yet use it in any rule, which leaves room for an exercise of your own.
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Four questions to ask before writing syntax
The article closes by recommending a set of prompts for any new model. They are not a formal checklist, but they are a practical habit:
- What entities exist in this problem?
- What state does each entity hold?
- Does each operation change that state or only read it?
- What rules prevent the state from becoming invalid?
Applied to the car, the answers are: a car, its speed, fuel, and engine state; the engine state and speed change under commands, while the speed check only reads; and the engine must be running before the car can accelerate.
Try it yourself
The article ends with a prompt worth taking seriously: “How would you explain variables and assignment to a complete beginner without using the word “variable”?” Try writing an explanation that uses a sandwich, a labeled box, or a bank balance, then check whether a beginner could follow it with no further help.
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- It is one author’s teaching account. The exercise was run in an engineering mentorship program with an apprentice named John. The article does not report a research design, measured outcomes, or a comparison showing that the method improves learning. No statistic on effectiveness is given.
- The criticism of beginner tutorials is opinion. The article’s view of “tutorial hell” is the author’s, not a measured finding.
- It covers one slice of object-oriented design. Microsoft Learn’s Object-Oriented programming (C#) tutorial also covers abstraction, encapsulation, inheritance, and polymorphism, none of which the sandwich exercise addresses.
- The physical model is deliberately weak. The plus-sign version is meant to show missing steps, not to suggest that addition is flawed.
- The plate comparison is a metaphor. It helps separate an object from its surroundings, but it is not an explanation of how memory is managed.
The original article is worth reading in full for its sequence of steps: We Reinvented OOP by Making a Sandwich (Before Writing Any Code), by Blessed Emmanuel John chidera, DEV Community, September 19, 2026.
Choosing further practice
If the sandwich-and-car approach works for you, a beginner C# or object-oriented programming book can supply the structured exercises the article leaves out. When comparing options, check four things: the stated level (complete beginner or prior programming experience), whether the book is specific to C# or language-neutral OOP, how exercises are presented, and whether you prefer print or free online material.
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