String to number conversion in Kotlin - Step-by-Step Execution

Concept Flow - String to number conversion

Start with String input

↓

Call conversion function

↓

Check if String is valid number

↓

Convert to number

↓

Use the number in code

↓

End

The program takes a string, tries to convert it to a number, checks if conversion is valid, then uses the number or handles errors.

Execution Sample

Kotlin

val str = "123"
val num = str.toInt()
println(num + 10)

Converts string "123" to integer 123 and adds 10, then prints 133.

Execution Table

Step	Action	Expression	Result	Notes
1	Assign string	str = "123"	"123"	String variable holds "123"
2	Convert string to int	num = str.toInt()	123	String "123" converts to integer 123
3	Add 10	num + 10	133	Integer 123 plus 10 equals 133
4	Print result	println(133)	133	Output is printed to console

💡 Conversion succeeds because "123" is a valid integer string

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
str	"123"	"123"	"123"	"123"
num	undefined	123	123	123

Key Moments - 2 Insights

What happens if the string is not a valid number?

If the string is not a valid number, calling toInt() throws a NumberFormatException. This is shown by the check in step 3 of the concept flow where invalid input leads to error.

Why do we need to convert the string before adding 10?

Adding 10 to a string would concatenate it as text, not add numerically. Conversion to int changes the type so arithmetic works, as shown in step 3 of the execution table.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'num' after step 2?

A 123

B "123"

C undefined

D 133

💡 Hint

Check the 'Result' column in row for step 2 in execution_table

At which step is the string converted to a number?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for conversion

If the string was "abc", what would happen at step 2?

A num becomes 0

B Program throws NumberFormatException

C num becomes "abc"

D num becomes null

💡 Hint

Refer to key_moments about invalid string conversion

Concept Snapshot

String to number conversion in Kotlin:
- Use toInt(), toDouble(), etc. to convert strings
- Conversion throws error if string is invalid
- Convert before arithmetic to get numeric results
- Handle exceptions for safe conversion

Full Transcript

This example shows how Kotlin converts a string "123" to an integer using toInt(). The program assigns the string, converts it to number, adds 10, and prints 133. If the string is invalid, toInt() throws an error. Conversion is necessary to perform arithmetic instead of string concatenation.