Answer: 10 Odd numbers from 1 to 20 are 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 — exactly 10 numbers.

Answer: 54321 The while prints i then decrements, while i 0: prints 5, 4, 3, 2, 1. After i becomes 0, condition is false. Output is "54321".

Answer: 15 The loop adds 1+2+3+4+5 = 15 to sum.

AP Computer Science A · Topic 4.2

for Loops Practice

Part of Iteration.

Practice questions

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Sample questions

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Sample 1difficulty 2/5
```
int count = 0;
for (int i = 1; i <= 20; i++) {
  if (i % 2 == 1) {
    count++;
  }
}
System.out.println(count);
```
$What is printed?$
- A
  $10$
  check_circle
- B
  $11$
- C
  $20$
- D
  $9$
Why
$Odd numbers from 1 to 20 are 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 — exactly 10 numbers.$
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Sample 2difficulty 2/5
```
int i = 5;
while (i > 0) {
  System.out.print(i);
  i--;
}
```
$What is printed?$
- A
  $12345$
- B
  $54321$
  check_circle
- C
  $5432$
- D
  $01234$
Why
$The while prints i then decrements, while i > 0: prints 5, 4, 3, 2, 1. After i becomes 0, condition is false. Output is "54321".$
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Sample 3difficulty 2/5
```
int sum = 0;
for (int i = 1; i <= 5; i++) {
  sum += i;
}
System.out.println(sum);
```
$What is printed?$
- A
  $15$
  check_circle
- B
  $10$
- C
  $14$
- D
  $21$
Why
$The loop adds 1+2+3+4+5 = 15 to sum.$
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Sample 4difficulty 2/5
```
public static void printReverse(int[] a) {
    for (int i = /* missing */; i >= 0; i--) {
        System.out.println(a[i]);
    }
}
```
$Which expression replaces /* missing */?$
- A
  $a.length - 1$
  check_circle
- B
  $a.length + 1$
- C
  $a.length$
- D
  $0$
Why
$The last valid index is a.length - 1. Iterate downward from there to 0.$
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Sample 5difficulty 2/5
```
int sum = 0;
for (int i = 0; i <= 10; i += 2) {
  sum += i;
}
System.out.println(sum);
```
$What is printed?$
- A
  $30$
  check_circle
- B
  $25$
- C
  $20$
- D
  $55$
Why
$i takes values 0, 2, 4, 6, 8, 10. Sum = 0+2+4+6+8+10 = 30.$
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