Parsing input to numeric types in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Parsing input to numeric types

Read input as string

↓

Try to convert string to number

↓

Store number

↓

Use number

The program reads input as text, tries to convert it to a number, and either stores the number or shows an error if conversion fails.

Execution Sample

C Sharp (C#)

string input = Console.ReadLine();
if (int.TryParse(input, out int number))
{
    Console.WriteLine(number);
}
else
{
    Console.WriteLine("Invalid input");
}

Reads a line from the user, tries to convert it to an integer, prints the number if successful, or prints an error message if not.

Execution Table

Step	Input String	TryParse Result	Parsed Number	Output
1	"123"	True	123	123
2	"abc"	False	0	Invalid input
3	"45.6"	False	0	Invalid input
4	"-789"	True	-789	-789
5	""	False	0	Invalid input

💡 Execution stops after printing output for each input string.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5
input	null	"123"	"abc"	"45.6"	"-789"	""
number	0	123	0	0	-789	0
TryParse Result	false	true	false	false	true	false

Key Moments - 3 Insights

Why does TryParse return false for "45.6" even though it looks like a number?

TryParse for int only accepts whole numbers without decimals. "45.6" has a decimal point, so it fails as shown in row 3 of the execution_table.

What happens to the 'number' variable when TryParse fails?

When TryParse returns false, 'number' is set to 0 by default, as seen in rows 2, 3, and 5 of the execution_table.

Why do we use TryParse instead of Parse directly?

TryParse safely attempts conversion without throwing an error if input is invalid, allowing the program to handle errors gracefully, as shown by the conditional branches in the code.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output when input is "-789"?

A "Invalid input"

B "-789"

C "0"

D No output

💡 Hint

Check row 4 in the execution_table under Output column.

At which step does TryParse return false?

A Step 2, Step 3, and Step 5

B Step 1 and Step 4

C Step 3 only

D All steps

💡 Hint

Look at the TryParse Result column in the execution_table.

If input is changed from "123" to "123abc", what would TryParse return?

A True

B Throws exception

C False

D Returns null

💡 Hint

TryParse returns false if the string contains non-numeric characters, similar to "abc" in row 2.

Concept Snapshot

Parsing input to numeric types in C#:
- Use int.TryParse(string, out int) to convert safely.
- Returns true if conversion succeeds, false otherwise.
- On failure, output variable is set to 0.
- Avoids exceptions from invalid input.
- Use conditional to handle success or error message.

Full Transcript

This example shows how to read user input as a string and convert it to an integer safely using int.TryParse in C#. The program tries to convert the input string to a number. If successful, it prints the number. If not, it prints "Invalid input". The execution table traces different inputs, showing when TryParse succeeds or fails and what output is printed. Variables like input, number, and TryParse result change step by step. Key moments clarify why decimal numbers fail and why TryParse is safer than Parse. The quiz tests understanding of outputs and TryParse behavior. This helps beginners see exactly how input parsing works in C#.