ITPEC FE Morning April 2019 Question 8
The flowchart below shows the algorithm of concatenating two character strings in X and Y, with the resulting character string in Z. Which of the following is the appropriate pair of operations to insert in the blanks, A and B? Here, X and Y are character arrays of dimensions m and n, respectively, where the i-th character of each string is stored as the i-th element of the character array.
Note:
The description in Loop 1 indicates that variable k varies from 1 to m by 1. So does Loop 2.
Explanation
A: X(k) → Z(k), B: Y(k) → Z(m+k) — copy X to the front of Z, then place Y directly after it.
- •Loop 1 runs k from 1 to m, the length of X, so it must copy X: X(k) goes to Z(k), filling Z(1) to Z(m)
- •Loop 2 runs k from 1 to n, the length of Y, so it copies Y, starting right after the last character of X: Y(k) goes to Z(m + k), filling Z(m + 1) to Z(m + n)
Answer (a)
Why not others:
- •(b) — offsets Y by n, its own length; unless m = n this overwrites the end of X or leaves a gap after it
- •(c) and (d) — copy Y in Loop 1, which runs to m, the length of X; they also put Y before X, which reverses the concatenation
Key rule: When appending one array to another, the second array's index in the result is offset by the length of the first; each loop's bound tells you which array it walks.
Algorithm and Programming · AI-written, may contain errors
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