Answer: Inner loop redeclares i; that variable is already in the enclosing scope Java disallows declaring a variable with the same name as one already in an enclosing block. Rename the inner variable, e.g., j.

Answer: 18 Inner loop sums 1+2+3 = 6. Outer loop runs 3 times, so total = 6 3 = 18.

Answer: 14 i=1: j=1,2,3 - 6. i=2: j=2,3 - 5. i=3: j=3 - 3. Total = 6 + 5 + 3 = 14.

AP Computer Science A · Topic 4.4

Nested Iteration Practice

Part of Iteration.

Practice questions

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Sample questions

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Sample 1difficulty 3/5
```
for (int i = 0; i < 3; i++) {
    for (int i = 0; i < 3; i++) {
        System.out.println("x");
    }
}
```
$What is wrong?$
- A
  $Compile-time inference fails$
- B
  $Nothing is wrong$
- C
  $Both loops share i and run nine times correctly$
- D
  $Inner loop redeclares i; that variable is already in the enclosing scope$
  check_circle
Why
$Java disallows declaring a variable with the same name as one already in an enclosing block. Rename the inner variable, e.g., j.$
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Sample 2difficulty 3/5
```
int sum = 0;
for (int i = 1; i <= 3; i++) {
  for (int j = 1; j <= 3; j++) {
    sum += j;
  }
}
System.out.println(sum);
```
$What is printed?$
- A
  $18$
  check_circle
- B
  $6$
- C
  $9$
- D
  $27$
Why
$Inner loop sums 1+2+3 = 6. Outer loop runs 3 times, so total = 6 * 3 = 18.$
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Sample 3difficulty 3/5

public static int run() {
    int s = 0;
    for (int i = 1; i <= 3; i++) {
        for (int j = i; j <= 3; j++) {
            s += j;
        }
    }
    return s;
}
// Call: System.out.println(run());

What is printed?

A
$18$
B
$12$
C
$9$
D
$14$
check_circle

Why

i=1: j=1,2,3 -> 6. i=2: j=2,3 -> 5. i=3: j=3 -> 3. Total = 6 + 5 + 3 = 14.

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Sample 4difficulty 3/5
```
int count = 0;
for (int i = 0; i < 3; i++) {
  for (int j = 0; j < 4; j++) {
    count++;
  }
}
System.out.println(count);
```
$What is printed?$
- A
  $7$
- B
  $12$
  check_circle
- C
  $16$
- D
  $9$
Why
$Outer loop runs 3 times, inner loop runs 4 times each. Total iterations = 3 * 4 = 12.$
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Sample 5difficulty 3/5

public static int run() {
    int s = 0;
    for (int i = 0; i < 5; i++) {
        if (i == 3) continue;
        s += i;
    }
    return s;
}
// Call: System.out.println(run());

What is printed?

A
$7$
check_circle
B
$8$
C
$10$
D
$6$

Why

Sum 0+1+2+4 = 7 (skipping 3).

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