In C, the code below reverses the first user argument character-by-character using strlen and a countdown index. If executed as: cmd> sample one two three, what does it print? /* sample.c */ #include<stdio.h> #include<string.h> int main(int argc, char *argv[]) { int i = 0; i += strlen(argv[1]); while(i > 0) { printf("%c", argv[1][--i]); } return 0; }

Introduction / Context: This tests string indexing and off-by-one care when reversing a string. The loop begins with i equal to the length of argv[1] and decrements before indexing, ensuring the last valid index is printed first.

Given Data / Assumptions:

• argv[1] is "one".
• i starts at strlen("one") = 3.
• Loop prints argv[1][--i] until i == 0.

Concept / Approach: Using pre-decrement inside the subscript shifts i from 3 to 2 for the first character printed, so the sequence of indices is 2, 1, 0 mapping to 'e', 'n', 'o' respectively, yielding the reverse string "eno".

Step-by-Step Solution:

Verification / Alternative check: Rewriting the loop to run i from strlen-1 down to 0 with i-- prints the same characters in the same order.

Why Other Options Are Wrong:

• owt / eerht: Those are reversals of "two" or "three", not "one".
• three two one: The program prints characters of argv[1] only, not words.
• noe: That is an incorrect reordering.

Common Pitfalls: Using post-decrement in the wrong place (argv[1][i--]) can cause off-by-one errors or print an extra character beyond bounds.

Final Answer: eno