VLSI DV Interview Puzzles · All levels

putc/getc Index Semantics

After one character replacement, what are final string, length, and ASCII code?

Puzzle

Difficulty: Medium · Puzzle 2 of 6 · Topic: String and Casting Puzzles

After one character replacement, what are final string, length, and ASCII code?

Code

systemverilog

module p2;
  string s = "dv puzzle";
  int ch;
  initial begin
    s.putc(3, 8'h5f); // '_'
    ch = s.getc(4);
    $display("s=%s len=%0d ch=%0d", s, s.len(), ch);
  end
endmodule

Hint

String indexing is zero-based and `putc` writes at an index, it does not insert and shift.

Step-by-step solution

diagram

1) Original index 3 is character `p` in `"dv puzzle"`.
2) `putc(3,'_')` replaces `p`, giving `"dv _uzzle"`.
3) Length remains 9 because replacement is in-place.
4) Index 4 is `u`, whose ASCII code is 117.

Answer

Answer: s=dv _uzzle, len=9, ch=117

Why candidates get it wrong

Many candidates treat `putc` like insertion and incorrectly change length/index mapping.

Interviewer follow-up

What does `s.getc(100)` return for out-of-range index?

Navigate