Output formatting basics in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print a formatted string with a name.

Go

package main
import "fmt"
func main() {
    name := "Alice"
    fmt.Printf("Hello, [1]!\n", name)
}

Drag options to blanks, or click blank then click option'

A"%v"

B"%d"

C"%f"

D"%s"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d instead of %s causes wrong output or errors.

Forgetting to include quotes around the format specifier.

The %s verb formats a string in Go's fmt.Printf function.

2fill in blank

medium

Complete the code to print a floating-point number with two decimal places.

Go

package main
import "fmt"
func main() {
    pi := 3.14159
    fmt.Printf("Pi is approximately [1]\n", pi)
}

Drag options to blanks, or click blank then click option'

A"%.2f"

B"%d"

C"%s"

D"%v"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d for floats causes wrong output.

Using %s prints the float as a string, not formatted.

The %.2f verb formats a float with two decimal places.

3fill in blank

hard

Fix the error in the code to print an integer with leading zeros to make it 5 digits.

Go

package main
import "fmt"
func main() {
    num := 42
    fmt.Printf("Number: [1]\n", num)
}

Drag options to blanks, or click blank then click option'

A"%05d"

B"%5d"

C"%d"

D"%f"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %5d pads with spaces, not zeros.

Using %f for integers causes errors.

The %05d verb prints an integer padded with zeros to width 5.

4fill in blank

hard

Fill both blanks to print a string left-aligned in a 10-character wide field and an integer right-aligned in a 5-character wide field.

Go

package main
import "fmt"
func main() {
    name := "Bob"
    age := 30
    fmt.Printf("Name: [1] Age: [2]\n", name, age)
}

Drag options to blanks, or click blank then click option'

A"%-10s"

B"%10s"

C"%5d"

D"%-5d"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %10s for string aligns right, not left.

Using %-5d left-aligns integer, but question wants right-aligned.

Use %-10s for left-aligned string in 10 spaces and %5d for right-aligned integer in 5 spaces.

5fill in blank

hard

Fill all three blanks to print a float with 3 decimals, a string right-aligned in 8 spaces, and an integer padded with zeros to 4 digits.

Go

package main
import "fmt"
func main() {
    price := 9.87654
    product := "Pen"
    code := 7
    fmt.Printf("Price: [1] Product: [2] Code: [3]\n", price, product, code)
}

Drag options to blanks, or click blank then click option'

A"%.3f"

B"%8s"

C"%04d"

D"%-8s"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %s without width does not align string.

Using %d without zero padding for code.

Use %.3f for float with 3 decimals, %8s for right-aligned string in 8 spaces, and %04d for zero-padded 4-digit integer.

Practice

1. What does the %d format specifier do in fmt.Printf in Go?

easy

A. Prints an integer value

B. Prints a floating-point number

C. Prints a string

D. Prints a boolean value

Solution

1. Step 1: Understand format specifiers in Go

   The %d specifier is used to print decimal integers in Go's fmt.Printf.

2. Step 2: Match specifier to data type

   Since %d prints integers, it matches integer values, not floats, strings, or booleans.

3. Final Answer:

   Prints an integer value -> Option A

4. Quick Check:

   %d = integer [OK]

Hint: Remember %d is for decimal integers in printf [OK]

Common Mistakes:

• Confusing %d with %f for floats
• Using %d for strings
• Thinking %d prints booleans

2. Which of the following is the correct syntax to print a string variable name using fmt.Printf in Go?

easy

A. fmt.Printf("%d", name)

B. fmt.Printf("%f", name)

C. fmt.Printf("%s", name)

D. fmt.Printf(name)

Solution

1. Step 1: Identify the correct format specifier for strings

   The format specifier for strings in Go's fmt.Printf is %s.

2. Step 2: Check the syntax correctness

   fmt.Printf("%s", name) uses fmt.Printf("%s", name), which correctly prints the string variable name.

3. Final Answer:

   fmt.Printf("%s", name) -> Option C

4. Quick Check:

   %s prints strings [OK]

Hint: Use %s for strings in fmt.Printf [OK]

Common Mistakes:

• Using %d or %f for strings
• Omitting quotes around format string
• Passing variable without format specifier

3. What is the output of the following Go code?

package main
import "fmt"
func main() {
    x := 7
    y := 3.14
    fmt.Printf("x = %d, y = %.1f\n", x, y)
}

medium

A. x = 7, y = 3.1

B. x = 7, y = 3.14

C. x = 7, y = 3.0

D. x = 7, y = 3

Solution

1. Step 1: Understand the format specifiers used

   %d prints integer x as 7. %.1f prints floating-point y rounded to 1 decimal place.

2. Step 2: Apply rounding to y

   3.14 rounded to 1 decimal place is 3.1, so output is "x = 7, y = 3.1".

3. Final Answer:

   x = 7, y = 3.1 -> Option A

4. Quick Check:

   %.1f rounds float to 1 decimal [OK]

Hint: %.1f rounds float to 1 decimal place [OK]

Common Mistakes:

• Expecting full float without rounding
• Confusing %d with %f
• Ignoring newline character

4. Identify the error in this Go code snippet:

package main
import "fmt"
func main() {
    name := "Alice"
    age := 30
    fmt.Printf("Name: %s, Age: %f\n", name, age)
}

medium

A. Missing newline character in format string

B. Missing import statement

C. Incorrect variable declaration

D. Using %f to print an integer variable

Solution

1. Step 1: Check format specifiers against variable types

   name is a string, printed with %s correctly. age is an integer but printed with %f, which expects a float.

2. Step 2: Identify the mismatch causing error

   Using %f for an integer causes a runtime error or incorrect output.

3. Final Answer:

   Using %f to print an integer variable -> Option D

4. Quick Check:

   Match %f with float, not int [OK]

Hint: Match %f only with float variables [OK]

Common Mistakes:

• Using %f for integers
• Ignoring type mismatch warnings
• Assuming %f works for all numbers

5. You want to print a table of product names and prices aligned in columns using fmt.Printf. Which format string correctly aligns the name left in 10 spaces and price right in 6 spaces with 2 decimals?

fmt.Printf("...", name, price)

hard

A. "%10s %-6.2f\n"

B. "%-10s %6.2f\n"

C. "%10s %6.2f\n"

D. "%-10s %-6.2f\n"

Solution

1. Step 1: Understand alignment flags in format strings

   In Go, %-10s means left-align string in 10 spaces; %6.2f means right-align float in 6 spaces with 2 decimals.

2. Step 2: Match alignment to requirements

   We want product name left-aligned in 10 spaces and price right-aligned in 6 spaces with 2 decimals, so "%-10s %6.2f\n" fits.

3. Final Answer:

   "%-10s %6.2f\n" -> Option B

4. Quick Check:

   Left-align string with %-10s, right-align float with %6.2f [OK]

Hint: Use - for left-align strings, no - for right-align numbers [OK]

Common Mistakes:

• Swapping alignment flags
• Using wrong width or precision
• Forgetting to specify decimal places for floats