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C# StringBuilder – 2 Questions per Major API (Moderate–High)

This sheet focuses on performance-aware and scenario-based coding questions using System.Text.StringBuilder.

Append

  1. Build a transaction log from 1 million messages without memory pressure.
  2. Read words until "STOP" and build the sentence efficiently.

AppendLine

  1. Generate a multi-line error report.
  2. Format stack-trace style output.

AppendFormat

  1. Build an invoice statement using placeholders.
  2. Create aligned columns for console output.

Insert

  1. Insert commas every 3 digits.
  2. Inject timestamps at the beginning of each log entry.

Remove

  1. Remove sensitive tokens by index.
  2. Delete alternate characters.

Replace

  1. Mask credit-card numbers.
  2. Replace forbidden chat words.

Clear

  1. Reuse builder inside loops.
  2. Reset CSV buffer after every row.

ToString

  1. Convert large builder to output chunks.
  2. Produce immutable snapshots.

Capacity

  1. Pre-allocate capacity for imports.
  2. Log resizing events.

EnsureCapacity

  1. Reserve memory before appending.
  2. Optimize JSON building for known size.

Length

  1. Truncate output beyond 10,000 chars.
  2. Validate maximum XML size.

CopyTo

  1. Copy part into a char buffer.
  2. Stream content into a file writer.

Equals

  1. Compare two builders for content equality.
  2. Detect identical logs.

AppendJoin

  1. Join thousands of values efficiently.
  2. Build pipe-separated exports.

Append(char, int)

  1. Generate padding spaces.
  2. Build ASCII boxes.

Insert(int, string)

  1. Inject separators into phone numbers.
  2. Add markers at specific indices.

Remove(int, int)

  1. Strip HTML tags by index ranges.
  2. Delete invalid data blocks.

Replace(string, string)

  1. Convert markup tags to HTML entities.
  2. Replace environment tokens.