Output formatting basics in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go code using fmt.Printf?

Consider the following Go code snippet. What will it print to the console?

Go

package main

import "fmt"

func main() {
    x := 42
    y := 3.14159
    fmt.Printf("x = %d, y = %.2f\n", x, y)
}

A x = 42, y = 3.1416

B x = 42, y = 3.14159

C x = 42, y = 3.14

D x = 42, y = 3.1

💡 Hint

Look at the %.2f format specifier. It controls how many decimal places are shown.

The %.2f format prints the floating-point number rounded to 2 decimal places. So 3.14159 becomes 3.14.

❓ Predict Output

intermediate

What does this Go code print with width formatting?

What is the output of this Go program that uses width specifiers in fmt.Printf?

Go

package main

import "fmt"

func main() {
    name := "Go"
    fmt.Printf("|%10s|%-10s|\n", name, name)
}

A | Go|Go |

B |Go | Go|

C | Go |Go |

D | Go| Go|

💡 Hint

The %10s means right-align in 10 spaces, %-10s means left-align in 10 spaces.

The first %10s prints the string right-aligned in 10 spaces, so spaces come first. The second %-10s prints left-aligned, so spaces come after.

❓ Predict Output

advanced

What is the output of this Go code using fmt.Sprintf with multiple verbs?

What string does this Go code produce?

Go

package main

import "fmt"

func main() {
    s := fmt.Sprintf("%d + %d = %d", 7, 5, 7+5)
    fmt.Println(s)
}

A 7 + 5 = 0

B 7 + 5 = 7+5

C 7 + 5 = 75

D 7 + 5 = 12

💡 Hint

fmt.Sprintf formats the string with the given values replacing %d verbs.

Each %d is replaced by the corresponding integer argument. So 7, 5, and 12 (7+5) are inserted.

❓ Predict Output

advanced

What error does this Go code produce?

What happens when you run this Go code?

Go

package main

import "fmt"

func main() {
    fmt.Printf("%d %s", 10)
}

A 10 %s

B runtime error: missing argument for %s

C 10

D Compilation error: wrong number of arguments

💡 Hint

Check if the number of verbs matches the number of arguments.

The format string expects two arguments (%d and %s), but only one (10) is given. This causes a runtime error.

🧠 Conceptual

expert

How many items are printed by this Go code with fmt.Printf and a slice?

What is the output count of items printed by this Go code snippet?

Go

package main

import "fmt"

func main() {
    nums := []int{1, 2, 3}
    fmt.Printf("%v %v %v %v", nums[0], nums[1], nums[2], nums)
}

A Prints 4 items: 1 2 3 [1 2 3]

B Prints 3 items: 1 2 3

C Prints 1 item: [1 2 3]

D Compilation error: cannot print slice with %v

💡 Hint

Each %v corresponds to one argument. The last argument is the whole slice.

The code prints four items: the three integers and then the slice printed as [1 2 3].

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