String Traversal and Character Access in DSA C# - Build from Scratch

String Traversal and Character Access

📖 Scenario: You work at a company that processes customer feedback messages. Each message is a string, and you need to analyze the characters inside it.

🎯 Goal: Build a simple program that goes through a given feedback message string, accesses each character one by one, and prints them out separately.

📋 What You'll Learn

Create a string variable with a specific feedback message

Create a variable to hold the length of the string

Use a for loop to traverse the string using the length variable

Access each character by its index inside the loop

Print each character on a new line

💡 Why This Matters

🌍 Real World

Processing and analyzing text messages, feedback, or any user input often requires going through each character to check or transform data.

💼 Career

Understanding string traversal is fundamental for roles in software development, data processing, and quality assurance where text manipulation is common.

1

Create the feedback message string

Create a string variable called feedback and set it to the exact value "Great product!"

DSA C#

# Your code here

Hint

Use string feedback = "Great product!"; to create the string variable.

2

Create a variable for the string length

Create an integer variable called length and set it to the length of the string feedback using feedback.Length

DSA C#

string feedback = "Great product!";
# Your code here

Hint

Use int length = feedback.Length; to get the string length.

3

Traverse the string using a for loop

Write a for loop with an integer variable i starting at 0, running while i < length, and increasing i by 1 each time

DSA C#

string feedback = "Great product!";
int length = feedback.Length;
# Your code here

Hint

Use for (int i = 0; i < length; i++) to loop through the string indices.

4

Print each character in the string

Inside the for loop, print the character at index i of feedback using Console.WriteLine(feedback[i])

DSA C#

string feedback = "Great product!";
int length = feedback.Length;
for (int i = 0; i < length; i++)
{
    // Print character at index i
    # Your code here
}

Hint

Use Console.WriteLine(feedback[i]); inside the loop to print each character on its own line.

Practice

1. What does the expression str[2] return when string str = "hello";?

easy

A. The character 'o'

B. The character 'l'

C. The character 'e'

D. An error because strings cannot be indexed

Solution

1. Step 1: Understand zero-based indexing in strings

   In C#, string characters are accessed starting from index 0. So, str[0] = 'h', str[1] = 'e', str[2] = 'l'.

2. Step 2: Identify the character at index 2

   The character at index 2 in "hello" is 'l'.

3. Final Answer:

   The character 'l' -> Option B

4. Quick Check:

   str[2] = 'l' [OK]

Hint: Remember string indexing starts at 0 in C# [OK]

Common Mistakes:

• Thinking indexing starts at 1
• Confusing characters at index 1 and 2
• Assuming strings can't be indexed

2. Which of the following is the correct way to loop through each character in a string str in C#?

easy

A. for (char c = 0; c < str.Length; c++) { Console.WriteLine(str[c]); }

B. for (int i = 1; i <= str.Length; i++) { Console.WriteLine(str[i]); }

C. foreach (int c in str) { Console.WriteLine(c); }

D. for (int i = 0; i < str.Length; i++) { Console.WriteLine(str[i]); }

Solution

1. Step 1: Check loop indexing and range

   In C#, string indexing starts at 0 and goes up to Length - 1. So the loop must run from 0 to str.Length - 1.

2. Step 2: Validate each option

   for (int i = 0; i < str.Length; i++) { Console.WriteLine(str[i]); } uses correct indexing (0 to Length-1). for (int i = 1; i <= str.Length; i++) { Console.WriteLine(str[i]); } starts at 1 and uses <= which causes out-of-range error. foreach (int c in str) { Console.WriteLine(c); } tries to foreach over int, but string yields chars, so type mismatch. for (char c = 0; c < str.Length; c++) { Console.WriteLine(str[c]); } uses char as loop variable which is incorrect.

3. Final Answer:

   for (int i = 0; i < str.Length; i++) { Console.WriteLine(str[i]); } -> Option D

4. Quick Check:

   Loop from 0 to Length-1 for string traversal [OK]

Hint: Use for loop with i from 0 to str.Length - 1 [OK]

Common Mistakes:

• Starting loop at 1 instead of 0
• Using <= instead of < in loop condition
• Using wrong variable type in foreach

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

string s = "code";
for (int i = 0; i < s.Length; i++)
{
    if (i % 2 == 0)
        Console.Write(s[i]);
}

medium

A. co

B. oe

C. cd

D. code

Solution

1. Step 1: Understand the loop and condition

   The loop runs from i=0 to i=3 (length 4). It prints characters only when i is even (0, 2).

2. Step 2: Identify characters at even indices

   At i=0, s[0] = 'c'; at i=2, s[2] = 'd'. So output is "cd".

3. Final Answer:

   cd -> Option C

4. Quick Check:

   Print chars at even indices: 'c' and 'd' [OK]

Hint: Print characters where index % 2 == 0 [OK]

Common Mistakes:

• Confusing even and odd indices
• Printing all characters ignoring condition
• Misreading string length

4. Identify the error in the following code snippet:

string text = "example";
for (int i = 0; i <= text.Length; i++)
{
    Console.Write(text[i]);
}

medium

A. The loop condition should be < instead of <=

B. The string cannot be indexed with []

C. Variable i should be of type char

D. Console.Write should be Console.WriteLine

Solution

1. Step 1: Analyze loop condition and indexing

   The loop runs from i=0 to i <= text.Length. Since string indices go from 0 to Length-1, accessing text[Length] causes an error.

2. Step 2: Correct the loop condition

   Change condition to i < text.Length to avoid out-of-range exception.

3. Final Answer:

   The loop condition should be < instead of <= -> Option A

4. Quick Check:

   Loop must run from 0 to Length-1 [OK]

Hint: Use i < str.Length to avoid index out of range [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Assuming string indexing is 1-based
• Changing variable type unnecessarily

5. Given a string input, which code snippet correctly counts how many vowels (a, e, i, o, u) it contains?

hard

A. int count = 0;
foreach (char c in input.ToLower()) {
if ("aeiou".Contains(c)) count++;
}
Console.WriteLine(count);

B. int count = 0;
for (int i = 1; i <= input.Length; i++) {
if ("aeiou".Contains(input[i])) count++;
}
Console.WriteLine(count);

C. int count = 0;
foreach (int c in input) {
if ("aeiou".Contains((char)c)) count++;
}
Console.WriteLine(count);

D. int count = 0;
for (char c = 0; c < input.Length; c++) {
if ("aeiou".Contains(input[c])) count++;
}
Console.WriteLine(count);

Solution

1. Step 1: Check correct iteration over string characters

   int count = 0; foreach (char c in input.ToLower()) { if ("aeiou".Contains(c)) count++; } Console.WriteLine(count); uses foreach over chars in input.ToLower(), which is correct. int count = 0; for (int i = 1; i <= input.Length; i++) { if ("aeiou".Contains(input[i])) count++; } Console.WriteLine(count); uses 1-based indexing causing out-of-range error. int count = 0; foreach (int c in input) { if ("aeiou".Contains((char)c)) count++; } Console.WriteLine(count); uses foreach over int which is incorrect type. int count = 0; for (char c = 0; c < input.Length; c++) { if ("aeiou".Contains(input[c])) count++; } Console.WriteLine(count); uses char as loop variable which is invalid.

2. Step 2: Verify vowel check and counting

   int count = 0; foreach (char c in input.ToLower()) { if ("aeiou".Contains(c)) count++; } Console.WriteLine(count); checks if character is in "aeiou" string and increments count correctly.

3. Final Answer:

   Option A code snippet correctly counts vowels -> Option A

4. Quick Check:

   Use foreach char and check vowels with Contains [OK]

Hint: Use foreach char in lowercase string and Contains("aeiou") [OK]

Common Mistakes:

• Using wrong loop indices causing errors
• Incorrect variable types in loops
• Not converting string to lowercase before checking