You have completed the core topics for Unit 4: Iteration. This comprehensive mock exam blends while loops, for loops, string algorithms, and nested loops into a single 15-question test designed to mimic the difficulty of the AP Computer Science A exam.
Exam Tips:
- Trace carefully: Do not guess. Write out a trace table for variables before selecting an answer.
- Check bounds: Pay close attention to
<vs<=, and whether strings process tolength()orlength() - 1. - Watch the scope: Remember that loop variables declared in a
forloop header do not exist outside the loop.
Unit 4 Iteration Mock Exam
Question 1 of 15 | Score: 0
1. What is printed as a result of executing the following code segment?
int k = 10;
while (k > 0) {
System.out.print(k + " ");
k -= 3;
}
Correct Answer: A
k starts at 10 and decreases by 3 each iteration: 10, 7, 4, 1. When k becomes -2, the condition -2 > 0 is false, so the loop ends.2. Consider the following code segment:
int sum = 0;
for (int i = 0; i < 5; i++) {
sum += i;
}
System.out.println(i);
Correct Answer: D
The variable
i is declared in the for loop header. It only exists within the loop’s scope. Attempting to print it outside the loop causes a compilation error.3. What does the following method do?
public String process(String str) {
String res = "";
for (int i = 0; i < str.length(); i++) {
if (i % 2 == 0) {
res += str.substring(i, i + 1);
}
}
return res;
}
Correct Answer: C
The condition
i % 2 == 0 is true for indices 0, 2, 4, 6… meaning the method extracts and returns the characters located at the even indices of the string.4. How many times will the word “Hi” be printed?
for (int a = 0; a < 4; a++) {
for (int b = 1; b < 3; b++) {
System.out.println("Hi");
}
}
Correct Answer: B
The outer loop runs 4 times (a=0, 1, 2, 3). The inner loop runs 2 times (b=1, 2). Total executions = 4 * 2 = 8.
5. What value is stored in
result after the code executes?int result = 0;
int x = 5;
while (x > 5) {
result += x;
x--;
}
Correct Answer: A
The initial condition
5 > 5 is false. The loop body executes zero times, leaving result at its initial value of 0.6. Which algorithm computes the sum of the digits of a positive integer
num?
Correct Answer: B
Option B correctly isolates the rightmost digit using
% 10, adds it to the sum, and then removes it from the number using integer division / 10.7. What is printed by the following code?
for(int i = 1; i <= 3; i++) {
for(int j = 1; j <= 3; j++) {
if(j >= i) System.out.print("*");
}
System.out.println();
}
Correct Answer: A
i=1: j prints * for 1, 2, 3 (***)
i=2: j prints * for 2, 3 (**)
i=3: j prints * for 3 (*)
The pattern decreases by one star each row.
i=2: j prints * for 2, 3 (**)
i=3: j prints * for 3 (*)
The pattern decreases by one star each row.
8. What does
val contain after the loop executes?int val = 0;
for(int i = 2; i < 10; i *= 2) {
val += i;
}
Correct Answer: B
i starts at 2 and multiplies by 2 each iteration: i=2, i=4, i=8. When i=16,
val = 2 + 4 + 8 = 14.
16 < 10 is false. val = 2 + 4 + 8 = 14.
9. What does the following code print?
String s = "Mississippi";
int c = 0;
for(int i = 0; i < s.length() - 1; i++) {
if(s.substring(i, i+2).equals("ss")) c++;
}
System.out.print(c);
Correct Answer: B
The loop checks for overlapping adjacent pairs matching “ss”. In “Mississippi”, the substring “ss” appears exactly twice.
10. How many times does
count++ execute?int count = 0;
for(int i = 0; i < 3; i++) {
for(int j = 0; j < 3; j++) {
if(i != j) count++;
}
}
Correct Answer: B
The inner loop executes 9 times total. The condition
i != j is true for every pair EXCEPT (0,0), (1,1), and (2,2). So it executes 9 – 3 = 6 times.11. Which of the following is equivalent to the code below?
for (int i = 0; i < 10; i++) { /* body */ }
Correct Answer: B
In a
for loop, the update expression (i++) executes *after* the body. Option B correctly replicates this logic by placing i++ at the very end of the while loop body.12. What is the value of
result?int result = 1;
for(int i = 4; i > 1; i--) {
result *= i;
}
Correct Answer: B
The loop multiplies: result = 1 * 4 = 4. Then 4 * 3 = 12. Then 12 * 2 = 24. When i=1,
1 > 1 is false. Output is 24.13. Which condition will prevent an infinite loop in the following structure?
int x = 10;
while (x ___ 0) {
x -= 2;
}
Correct Answer: B
Using
!= 0 can be risky if x misses 0 (e.g. if x started odd). However, x > 0 guarantees the loop terminates safely once x becomes 0 or negative.14. What does the following code print?
String w = "hello";
for(int i = w.length(); i > 0; i--) {
System.out.print(w.substring(i-1, i));
}
Correct Answer: B
i starts at 5. w.substring(4, 5) returns ‘o’. Next i=4, w.substring(3, 4) returns ‘l’. This is a standard reverse string loop, printing “olleh”.15. What is printed by this nested structure?
int c = 0;
for(int i = 0; i < 5; i++) {
for(int j = 0; j < i; j++) {
c++;
}
}
System.out.println(c);
Correct Answer: B
i=0: j<0 (0 times)
i=1: j<1 (1 time)
i=2: j<2 (2 times)
i=3: j<3 (3 times)
i=4: j<4 (4 times)
Total = 0 + 1 + 2 + 3 + 4 = 10.
i=1: j<1 (1 time)
i=2: j<2 (2 times)
i=3: j<3 (3 times)
i=4: j<4 (4 times)
Total = 0 + 1 + 2 + 3 + 4 = 10.
Unit 4 Mock Exam Complete!
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Congratulations on Completing Unit 4!
Iteration is arguably the most important foundational concept in all of computer science. By mastering while loops, for loops, and nested iteration, you now have the tools required to traverse data structures, process strings, and write complex algorithms.
Now that you know how to control the flow of your programs, it is time to learn how to design your own custom objects and behaviors. Continue your AP CSA journey by moving on to the next major module: Unit 5: Writing Classes.