Basic input concepts in Go - Step-by-Step Execution

Concept Flow - Basic input concepts

Start program

↓

Prompt user for input

↓

Wait for user to type

↓

User presses Enter

↓

Read input into variable

↓

Use input in program

↓

End program

The program starts, asks the user for input, waits for the user to type and press Enter, then reads and stores the input for use.

Execution Sample

Go

package main
import "fmt"
func main() {
  var name string
  fmt.Print("Enter your name: ")
  fmt.Scanln(&name)
  fmt.Println("Hello,", name)
}

This program asks the user to enter their name, reads it, and then greets them.

Execution Table

Step	Action	Input/Condition	Variable State	Output
1	Program starts	-	name = ""	-
2	Print prompt	-	name = ""	Enter your name:
3	Wait for user input	User types 'Alice' and presses Enter	name = ""	-
4	Read input into variable	-	name = "Alice"	-
5	Print greeting	-	name = "Alice"	Hello, Alice
6	Program ends	-	name = "Alice"	-

💡 Program ends after printing greeting.

Variable Tracker

Variable	Start	After Step 4	Final
name	""	"Alice"	"Alice"

Key Moments - 2 Insights

Why do we use &name in fmt.Scanln(&name)?

We use &name to pass the memory address of the variable so fmt.Scanln can store the input directly into it, as shown in step 4 of the execution_table.

What happens if the user just presses Enter without typing anything?

The variable 'name' will remain an empty string "", because fmt.Scanln reads what the user typed before Enter, as seen in step 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'name' after step 4?

A ""

B "Alice"

C nil

D "Enter your name:"

💡 Hint

Check the 'Variable State' column at step 4 in the execution_table.

At which step does the program print the greeting message?

A Step 5

B Step 4

C Step 2

D Step 6

💡 Hint

Look at the 'Output' column in the execution_table for the greeting message.

If the user inputs 'Bob' instead of 'Alice', which part of the execution_table changes?

A Step 5 output

B Step 2 output

C Step 3 and Step 4 variable state

D Step 1 action

💡 Hint

User input affects the variable state during reading input, see steps 3 and 4.

Concept Snapshot

Basic input in Go:
- Use fmt.Print to show prompt
- Use fmt.Scanln(&var) to read input
- &var passes variable address
- Input stored in variable for use
- Program continues after input

Full Transcript

This Go program starts by declaring a string variable 'name'. It prints a prompt asking the user to enter their name. The program then waits for the user to type and press Enter. Using fmt.Scanln with &name, it reads the input and stores it in the variable 'name'. Finally, it prints a greeting message including the entered name and ends. The key is passing the variable's address to read input correctly.