Use cases - Step-by-Step Execution

Concept Flow - Use cases

Start Program

↓

Define Use Case

↓

Implement Functionality

↓

Call Function in main()

↓

Observe Output

↓

End Program

This flow shows how a use case in C starts with defining a task, implementing it, calling it in main, and then observing the output.

Execution Sample

C

#include <stdio.h>

void greet() {
    printf("Hello, friend!\n");
}

int main() {
    greet();
    return 0;
}

This code defines a simple use case: greeting the user by printing a message.

Execution Table

Step	Action	Function Called	Output	Notes
1	Program starts	None		main() begins execution
2	Call greet()	greet		main calls greet function
3	Execute greet()	greet	Hello, friend!	greet prints message
4	Return to main()	None		greet finishes, back to main
5	Return 0 from main()	None		Program ends successfully

💡 Program ends after main returns 0

Variable Tracker

Variable	Start	After greet call	Final
None	N/A	N/A	N/A

Key Moments - 2 Insights

Why does the program print the message only after calling greet()?

Because the printf statement is inside greet(), which runs only when main() calls greet(), as shown in execution_table step 2 and 3.

What happens if we remove the greet() call from main()?

The message won't print because greet() never runs. The program would start and end without output, as no function prints anything.

Visual Quiz - 3 Questions

Look at the execution table, what is printed at step 3?

A Error message

B Hello, friend!

C No output

D greet function name

💡 Hint

Check the Output column at step 3 in the execution_table

At which step does the program return control back to main() after greet() finishes?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the Notes column for step 4 in execution_table

If we remove the greet() call from main(), what changes in the execution table?

A Step 5 changes to return 1

B Program crashes at step 2

C Step 3 output disappears

D Step 1 is skipped

💡 Hint

Refer to key_moments about what happens if greet() is not called

Concept Snapshot

Use cases in C show how to organize code for tasks.
Define a function for the task.
Call the function from main() to run it.
Output happens when function runs.
Program ends after main returns.

Full Transcript

This example shows a simple use case in C programming. The program starts in main(), which calls the greet() function. The greet() function prints a friendly message. After greet() finishes, control returns to main(), which then ends the program. If greet() is not called, no message prints. This flow helps beginners see how functions represent use cases and how calling them runs their code.