String to Integer atoi in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert the first character of the string to an integer digit.

DSA Go

digit := int(str[0] - '[1]')

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

A'1'

B'0'

C'9'

D'a'

Attempts:

3 left

💡 Hint

Common Mistakes

Using '1' or 'a' instead of '0' causes wrong conversion.

Subtracting the character '0' from a digit character gives its integer value.

2fill in blank

medium

Complete the code to check if the character is a digit.

DSA Go

if str[i] >= '[1]' && str[i] <= '9' {

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

A'0'

B'a'

C'A'

D'1'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'a' or 'A' instead of '0' causes wrong checks.

Digits in ASCII range from '0' to '9'.

3fill in blank

hard

Fix the error in the code to accumulate the integer value from digits.

DSA Go

result = result [1] 10 + int(str[i] - '0')

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' causes wrong accumulation.

Multiply the current result by 10 before adding the new digit.

4fill in blank

hard

Fill both blanks to correctly handle the sign and start index.

DSA Go

sign := 1
start := 0
if str[0] == '[1]' {
    sign = -1
    start = [2]
}

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

A'-'

B1

C2

D'+'

Attempts:

3 left

💡 Hint

Common Mistakes

Not updating start index after sign causes errors.

If the first character is '-', sign is -1 and start index moves to 1.

5fill in blank

hard

Fill all three blanks to complete the atoi function returning the integer value.

DSA Go

func atoi(str string) int {
    sign := 1
    result := 0
    start := 0
    if str[0] == '[1]' {
        sign = -1
        start = [2]
    }
    for i := start; i < len(str); i++ {
        if str[i] < '[3]' || str[i] > '9' {
            break
        }
        result = result*10 + int(str[i] - '0')
    }
    return sign * result
}

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

A'-'

B1

C'0'

D'+'

Attempts:

3 left

💡 Hint

Common Mistakes

Wrong start index or digit range causes incorrect parsing.

Check for '-' sign, start parsing from index 1, and ensure digits are between '0' and '9'.

Practice

1. What does the atoi function do in the context of strings and integers?

easy

A. Converts an integer into a string representation

B. Converts a string representing a number into an integer value

C. Checks if a string contains only digits

D. Splits a string into individual characters

Solution

1. Step 1: Understand the purpose of atoi

   The function atoi stands for ASCII to integer, meaning it converts a string of digits into an integer number.

2. Step 2: Compare options with definition

   Only Converts a string representing a number into an integer value correctly describes converting a numeric string to an integer value.

3. Final Answer:

   Converts a string representing a number into an integer value -> Option B

4. Quick Check:

   atoi converts string to int [OK]

Hint: Remember atoi means ASCII to integer conversion [OK]

Common Mistakes:

• Confusing atoi with integer to string conversion
• Thinking atoi splits strings
• Assuming atoi validates string digits only

2. Which of the following Go code snippets correctly converts the string "1234" to an integer using strconv.Atoi?

easy

A. num, err := strconv.Atoi("1234")

B. num := strconv.Atoi("1234")

C. num := strconv.Atoi(1234)

D. num, err := strconv.Atoi(1234)

Solution

1. Step 1: Check function signature of strconv.Atoi

   It returns two values: an integer and an error, so both must be captured.

2. Step 2: Verify argument type

   The argument must be a string, so "1234" is correct, not 1234 (int).

3. Final Answer:

   num, err := strconv.Atoi("1234") -> Option A

4. Quick Check:

   Correct syntax captures int and error [OK]

Hint: Always capture both int and error from strconv.Atoi [OK]

Common Mistakes:

• Not capturing the error return value
• Passing an integer instead of a string
• Using single return variable for two returns

3. What will be the output of the following Go code?

package main
import (
  "fmt"
  "strconv"
)
func main() {
  s := "-42"
  num, err := strconv.Atoi(s)
  if err != nil {
    fmt.Println("Error")
  } else {
    fmt.Println(num)
  }
}

medium

A. -42

B. 42

C. Error

D. 0

Solution

1. Step 1: Understand input string and conversion

   The string "-42" is a valid integer representation including a negative sign.

2. Step 2: Check error handling and output

   Since "-42" is valid, err will be nil and num will be -42, so it prints -42.

3. Final Answer:

   -42 -> Option A

4. Quick Check:

   Valid negative string converts to negative int [OK]

Hint: Negative strings convert correctly with atoi [OK]

Common Mistakes:

• Assuming negative sign causes error
• Expecting absolute value output
• Ignoring error check

4. Identify the error in the following Go code snippet that uses strconv.Atoi:

package main
import (
  "fmt"
  "strconv"
)
func main() {
  s := "12a4"
  num, _ := strconv.Atoi(s)
  fmt.Println(num)
}

medium

A. Missing import of strconv package

B. Using fmt.Println instead of fmt.Print

C. Passing a string with letters to strconv.Atoi is allowed

D. Ignoring the error returned by strconv.Atoi

Solution

1. Step 1: Analyze input string validity

   The string "12a4" contains a letter 'a', so it is not a valid integer string.

2. Step 2: Check error handling in code

   The code ignores the error by using underscore _, so it prints zero value 0 without warning.

3. Final Answer:

   Ignoring the error returned by strconv.Atoi -> Option D

4. Quick Check:

   Always check error when converting strings [OK]

Hint: Never ignore error from atoi, always check it [OK]

Common Mistakes:

• Assuming invalid strings convert to partial numbers
• Ignoring error causes silent wrong output
• Thinking fmt.Println usage is wrong

5. You want to convert a list of strings ["10", "-5", "abc", "20"] to integers using strconv.Atoi. Which approach correctly handles invalid strings and collects only valid integers?

hard

A. Use strconv.Atoi only on first string, ignore rest

B. Convert all strings without error check and append results directly

C. Loop over strings, convert each with strconv.Atoi, append to result only if error is nil

D. Convert strings to integers using strconv.Itoa

Solution

1. Step 1: Understand the problem requirements

   We must convert multiple strings to integers and skip invalid ones safely.

2. Step 2: Evaluate each option's correctness

   Loop over strings, convert each with strconv.Atoi, append to result only if error is nil correctly loops, converts, checks error, and appends valid integers only.

3. Final Answer:

   Loop over strings, convert each with strconv.Atoi, append to result only if error is nil -> Option C

4. Quick Check:

   Check error for each conversion before appending [OK]

Hint: Check error for each string before adding integer [OK]

Common Mistakes:

• Appending invalid conversions without error check
• Using strconv.Itoa which converts int to string
• Ignoring invalid strings completely