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Java Practice Questions

Topic-based coding problems with sample test cases — build confidence step by step.

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Java For Loop Practice

for loops: counting, summing, patterns, primes, series and string iteration.

1
Print 1 to N (For)
Easy
Read a positive integer N and print all integers from 1 to N, each on its own line, using a for loop.
Input Format
A single integer N.
Output Format
N lines: 1, 2, ..., N.
Sample Test Cases
Sample Input 1
3
Sample Output 1
1
2
3
Sample Input 2
1
Sample Output 2
1
Sample Input 3
5
Sample Output 3
1
2
3
4
5
Sample Input 4
2
Sample Output 4
1
2
Sample Input 5
10
Sample Output 5
1
2
3
4
5
6
7
8
9
10
Constraints
1
Explanation
for (int i = 1; i
2
Print N to 1 (For)
Easy
Read a positive integer N and print N, N-1, ..., 1, each on its own line, using a for loop.
Input Format
A single integer N.
Output Format
N lines: N, N-1, ..., 1.
Sample Test Cases
Sample Input 1
3
Sample Output 1
3
2
1
Sample Input 2
1
Sample Output 2
1
Sample Input 3
5
Sample Output 3
5
4
3
2
1
Sample Input 4
2
Sample Output 4
2
1
Sample Input 5
7
Sample Output 5
7
6
5
4
3
2
1
Constraints
1
Explanation
for (int i = n; i >= 1; i--) print i;
3
Sum of N Natural Numbers (For)
Easy
Read a positive integer N and print 1 + 2 + ... + N using a for loop.
Input Format
A single integer N.
Output Format
A single integer: the sum.
Sample Test Cases
Sample Input 1
10
Sample Output 1
55
Sample Input 2
5
Sample Output 2
15
Sample Input 3
1
Sample Output 3
1
Sample Input 4
100
Sample Output 4
5050
Sample Input 5
3
Sample Output 5
6
Constraints
1
Explanation
for (int i = 1; i
4
Multiplication Table (For)
Easy
Read an integer N and print its multiplication table from 1 to 10 using a for loop, one per line, in the format "N x i = product".
Input Format
A single integer N.
Output Format
10 lines of the form "N x i = product".
Sample Test Cases
Sample Input 1
5
Sample Output 1
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50
Sample Input 2
2
Sample Output 2
2 x 1 = 2
2 x 2 = 4
2 x 3 = 6
2 x 4 = 8
2 x 5 = 10
2 x 6 = 12
2 x 7 = 14
2 x 8 = 16
2 x 9 = 18
2 x 10 = 20
Sample Input 3
3
Sample Output 3
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 = 27
3 x 10 = 30
Constraints
1
Explanation
for (int i = 1; i
5
Sum of Even Numbers (For)
Easy
Read a positive integer N and print the sum of all even numbers from 1 to N using a for loop.
Input Format
A single integer N.
Output Format
A single integer: the sum of evens.
Sample Test Cases
Sample Input 1
10
Sample Output 1
30
Sample Input 2
5
Sample Output 2
6
Sample Input 3
1
Sample Output 3
0
Sample Input 4
2
Sample Output 4
2
Sample Input 5
100
Sample Output 5
2550
Constraints
1
Explanation
for (int i = 2; i
1
Factorial (For)
Medium
Read a non-negative integer N and print N! using a for loop.
Input Format
A single integer N.
Output Format
A single integer: N!.
Sample Test Cases
Sample Input 1
5
Sample Output 1
120
Sample Input 2
0
Sample Output 2
1
Sample Input 3
1
Sample Output 3
1
Sample Input 4
10
Sample Output 4
3628800
Sample Input 5
20
Sample Output 5
2432902008176640000
Constraints
0
Explanation
long f = 1; for (int i = 2; i
2
Count Digits (For)
Medium
Read a positive integer N and print the number of digits. Convert N to a string and use a for loop over its characters.
Input Format
A single integer N.
Output Format
A single integer: the digit count.
Sample Test Cases
Sample Input 1
12345
Sample Output 1
5
Sample Input 2
7
Sample Output 2
1
Sample Input 3
0
Sample Output 3
1
Sample Input 4
1000000000
Sample Output 4
10
Sample Input 5
999
Sample Output 5
3
Constraints
1
Explanation
String s = Integer.toString(n); for (int i = 0; i < s.length(); i++) count++;
3
Sum of Digits (For)
Medium
Read a positive integer N and print the sum of its digits. Use a for loop over the characters of its string form.
Input Format
A single integer N.
Output Format
A single integer: the digit sum.
Sample Test Cases
Sample Input 1
1234
Sample Output 1
10
Sample Input 2
999
Sample Output 2
27
Sample Input 3
1
Sample Output 3
1
Sample Input 4
1000000000
Sample Output 4
1
Sample Input 5
987654321
Sample Output 5
45
Constraints
1
Explanation
for (char c : Integer.toString(n).toCharArray()) sum += c - '0';
4
Armstrong Number (For)
Medium
Read a 3-digit integer N and print "Armstrong" if the sum of the cubes of its digits equals N, otherwise "Not Armstrong".
Input Format
A single integer N (100-999).
Output Format
"Armstrong" or "Not Armstrong".
Sample Test Cases
Sample Input 1
153
Sample Output 1
Armstrong
Sample Input 2
123
Sample Output 2
Not Armstrong
Sample Input 3
370
Sample Output 3
Armstrong
Sample Input 4
371
Sample Output 4
Armstrong
Sample Input 5
100
Sample Output 5
Not Armstrong
Constraints
100
Explanation
for each digit, cube it and add.
5
Prime Check (For)
Medium
Read an integer N > 1 and print "Prime" or "Not Prime". Use a for loop to test divisors.
Input Format
A single integer N.
Output Format
"Prime" or "Not Prime".
Sample Test Cases
Sample Input 1
17
Sample Output 1
Prime
Sample Input 2
15
Sample Output 2
Not Prime
Sample Input 3
2
Sample Output 3
Prime
Sample Input 4
97
Sample Output 4
Prime
Sample Input 5
100
Sample Output 5
Not Prime
Constraints
2
Explanation
for (int i = 2; i * i
6
Reverse a String (For)
Medium
Read a string and print it reversed using a for loop.
Input Format
A single line containing a string S (no spaces).
Output Format
The reversed string.
Sample Test Cases
Sample Input 1
hello
Sample Output 1
olleh
Sample Input 2
abc
Sample Output 2
cba
Sample Input 3
a
Sample Output 3
a
Sample Input 4
racecar
Sample Output 4
racecar
Sample Input 5
TechBridge24
Sample Output 5
42egdirBhceT
Constraints
1
Explanation
for (int i = s.length()-1; i >= 0; i--) append s.charAt(i).
7
Print Odd Numbers
Medium
Read a positive integer N and print all odd numbers from 1 to N on one line, space-separated, using a for loop.
Input Format
A single integer N.
Output Format
Odds from 1 to N on one line.
Sample Test Cases
Sample Input 1
9
Sample Output 1
1 3 5 7 9
Sample Input 2
6
Sample Output 2
1 3 5
Sample Input 3
1
Sample Output 3
1
Sample Input 4
2
Sample Output 4
1
Sample Input 5
15
Sample Output 5
1 3 5 7 9 11 13 15
Constraints
1
Explanation
for (int i = 1; i
1
Print Prime Numbers in Range (For)
Hard
Read N and print all prime numbers from 2 to N, space-separated on one line. If there are none, print "None".
Input Format
A single integer N.
Output Format
Primes from 2 to N on one line, or "None".
Sample Test Cases
Sample Input 1
10
Sample Output 1
2 3 5 7
Sample Input 2
20
Sample Output 2
2 3 5 7 11 13 17 19
Sample Input 3
2
Sample Output 3
2
Sample Input 4
50
Sample Output 4
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
Sample Input 5
3
Sample Output 5
2 3
Constraints
2
Explanation
Nested for loops: for each number test divisibility.
2
Fibonacci Series (For)
Hard
Read N and print the first N Fibonacci numbers (0, 1, 1, 2, ...) on one line, space-separated, using a for loop.
Input Format
A single integer N.
Output Format
The first N Fibonacci numbers on one line.
Sample Test Cases
Sample Input 1
7
Sample Output 1
0 1 1 2 3 5 8
Sample Input 2
3
Sample Output 2
0 1 1
Sample Input 3
1
Sample Output 3
0
Sample Input 4
10
Sample Output 4
0 1 1 2 3 5 8 13 21 34
Sample Input 5
5
Sample Output 5
0 1 1 2 3
Constraints
1
Explanation
for (int i = 0; i < n; i++) { print a; next = a + b; a = b; b = next; }
3
Number Pattern (Right Triangle)
Hard
Read N and print N rows. Row i contains 1..i separated by spaces, using a for loop.
Input Format
A single integer N.
Output Format
N lines; line i has numbers 1..i.
Sample Test Cases
Sample Input 1
3
Sample Output 1
1
1 2
1 2 3
Sample Input 2
1
Sample Output 2
1
Sample Input 3
4
Sample Output 3
1
1 2
1 2 3
1 2 3 4
Sample Input 4
2
Sample Output 4
1
1 2
Sample Input 5
5
Sample Output 5
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
Constraints
1
Explanation
for (int i = 1; i
4
Power Using Loop
Hard
Read two integers B and E (non-negative) and print B^E using a for loop (no Math.pow).
Input Format
A single line with two integers B and E.
Output Format
A single integer: B^E.
Sample Test Cases
Sample Input 1
2 10
Sample Output 1
1024
Sample Input 2
5 3
Sample Output 2
125
Sample Input 3
0 0
Sample Output 3
1
Sample Input 4
0 5
Sample Output 4
0
Sample Input 5
10 10
Sample Output 5
10000000000
Constraints
0
Explanation
long r = 1; for (int i = 0; i < e; i++) r *= b;
5
Sum of Series
Hard
Read a positive integer N and print the sum 1 - 2 + 3 - 4 + ... ± N (alternating signs).
Input Format
A single integer N.
Output Format
A single integer: the alternating sum.
Sample Test Cases
Sample Input 1
5
Sample Output 1
3
Sample Input 2
4
Sample Output 2
-2
Sample Input 3
1
Sample Output 3
1
Sample Input 4
2
Sample Output 4
-1
Sample Input 5
10
Sample Output 5
-5
Constraints
1
Explanation
for (int i = 1; i
6
Largest Digit (For)
Hard
Read a positive integer N and print its largest digit. Use a for loop over the characters of its string form.
Input Format
A single integer N.
Output Format
A single integer: the largest digit.
Sample Test Cases
Sample Input 1
2913
Sample Output 1
9
Sample Input 2
100
Sample Output 2
1
Sample Input 3
1
Sample Output 3
1
Sample Input 4
987654321
Sample Output 4
9
Sample Input 5
50505
Sample Output 5
5
Constraints
1
Explanation
for (char c : Integer.toString(n).toCharArray()) track max of (c - '0').
7
Star Pattern (Triangle)
Hard
Read N and print N rows. Row i contains i asterisks (*), using nested for loops.
Input Format
A single integer N.
Output Format
N lines; line i has i asterisks.
Sample Test Cases
Sample Input 1
3
Sample Output 1
*
**
***
Sample Input 2
1
Sample Output 2
*
Sample Input 3
4
Sample Output 3
*
**
***
****
Sample Input 4
2
Sample Output 4
*
**
Sample Input 5
5
Sample Output 5
*
**
***
****
*****
Constraints
1
Explanation
for (int i = 1; i
8
Count Divisors
Hard
Read a positive integer N and print the number of its positive divisors. Use a for loop.
Input Format
A single integer N.
Output Format
A single integer: the divisor count.
Sample Test Cases
Sample Input 1
12
Sample Output 1
6
Sample Input 2
7
Sample Output 2
2
Sample Input 3
1
Sample Output 3
1
Sample Input 4
100
Sample Output 4
9
Sample Input 5
16
Sample Output 5
5
Constraints
1
Explanation
for (int i = 1; i * i
Competitive MCQs — Java For Loop
Code snippets, output prediction, concepts & error spotting. Pick an answer to see instant feedback.
Score 0/ 38
Q1
What is the output of this code?
java
1
2
3
for (int i = 0; i < 3; i++) {
    System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
i runs 0,1,2 then 3 fails the test.
Q2
What is the output of this code?
for (int i = 0; i < 3; i++) {
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
i runs 0,1,2 then 3 fails the test.
Q3
Which part of a for loop is optional?
Correct!
Wrong — correct answer is .
for(;;) is valid; any or all parts may be empty.
Q4
What is the output of this code?
java
1
2
3
4
5
int s = 0;
for (int i = 1; i <= 4; i++) {
    s += i;
}
System.out.println(s);
Correct!
Wrong — correct answer is .
Sums 1+2+3+4 = 10.
Q5
What is the output of this code?
int s = 0;
for (int i = 1; i <= 4; i++) {
s += i;
}
System.out.println(s);
Correct!
Wrong — correct answer is .
Sums 1+2+3+4 = 10.
Q6
What is the output of this code?
java
1
2
3
for (int i = 10; i >= 8; i--) {
    System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
i counts down from 10 to 8.
Q7
What is the output of this code?
for (int i = 10; i >= 8; i--) {
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
i counts down from 10 to 8.
Q8
Which loop is best for iterating over all elements of an array?
Correct!
Wrong — correct answer is .
for (int v : arr) visits every element cleanly.
Q9
What is the output of this code?
java
1
2
3
4
5
int count = 0;
for (int i = 0; i < 10; i += 2) {
    count++;
}
System.out.println(count);
Correct!
Wrong — correct answer is .
i = 0,2,4,6,8 → five iterations.
Q10
What is the output of this code?
int count = 0;
for (int i = 0; i < 10; i += 2) {
count++;
}
System.out.println(count);
Correct!
Wrong — correct answer is .
i = 0,2,4,6,8 → five iterations.
Q11
What is the output of this code?
java
1
2
3
4
5
for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 2; j++) {
        System.out.print(i * j + " ");
    }
}
Correct!
Wrong — correct answer is .
Nested loop prints i*j for i=1..3, j=1..2.
Q12
What is the output of this code?
for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 2; j++) {
System.out.print(i * j + " ");
}
}
Correct!
Wrong — correct answer is .
Nested loop prints i*j for i=1..3, j=1..2.
Q13
What is the output of this code?
java
1
2
3
4
for (int i = 0; i < 5; i++) {
    if (i == 2) continue;
    System.out.print(i);
}
Correct!
Wrong — correct answer is .
continue skips printing when i == 2.
Q14
What is the output of this code?
for (int i = 0; i < 5; i++) {
if (i == 2) continue;
System.out.print(i);
}
Correct!
Wrong — correct answer is .
continue skips printing when i == 2.
Q15
Which loop body never runs in this code?
java
1
2
3
for (int i = 5; i < 3; i++) {
    System.out.println(i);
}
Correct!
Wrong — correct answer is .
The condition 5 < 3 is false from the start.
Q16
Which loop body never runs in this code?
for (int i = 5; i < 3; i++) {
System.out.println(i);
}
Correct!
Wrong — correct answer is .
The condition 5 < 3 is false from the start.
Q17
What is the output of this code?
java
1
2
3
4
5
int x = 1;
for (; x <= 3; ) {
    System.out.print(x + " ");
    x++;
}
Correct!
Wrong — correct answer is .
Omitted init/update still work with an external counter.
Q18
What is the output of this code?
int x = 1;
for (; x <= 3; ) {
System.out.print(x + " ");
x++;
}
Correct!
Wrong — correct answer is .
Omitted init/update still work with an external counter.
Q19
What is the output of this code?
for (int i = 5; i >= 1; i--) {
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
The loop counts down from 5 to 1.
Q20
What is the output of this code?
int sum = 0;
for (int i = 1; i <= 10; i += 2) {
sum += i;
}
System.out.println(sum);
Correct!
Wrong — correct answer is .
Odd numbers 1+3+5+7+9 = 25.
Q21
How many times does this loop print?
for (int i = 0; i < 4; i++) {
System.out.println(i);
}
Correct!
Wrong — correct answer is .
i runs 0, 1, 2, 3 — four iterations.
Q22
What is the output of this code?
for (int i = 2; i <= 8; i *= 2) {
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
i doubles 2→4→8, then 16 stops the loop.
Q23
What does the enhanced for loop iterate over?
Correct!
Wrong — correct answer is .
for (Type v : collection) visits every element.
Q24
What is the output of this code?
int[] a = {1, 2, 3};
for (int v : a) {
System.out.print(v * 2 + " ");
}
Correct!
Wrong — correct answer is .
Each element is doubled: 2, 4, 6.
Q25
What is the output of this code?
for (int i = 0; i < 5; i++) {
if (i % 2 == 0) continue;
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
continue skips even i, printing only odds 1 and 3.
Q26
What is the output of this code?
int count = 0;
for (int i = 1; i <= 100; i *= 10) {
count++;
}
System.out.println(count);
Correct!
Wrong — correct answer is .
i is 1, 10, 100 — three iterations.
Q27
Which loop is best for iterating an array by index?
Correct!
Wrong — correct answer is .
Index-based loops let you read and update specific positions.
Q28
What is the output of this code?
for (int i = 0, j = 10; i < 3; i++, j--) {
System.out.print((i + j) + " ");
}
Correct!
Wrong — correct answer is .
Each step pairs i with j so i + j stays 10.
Q29
What is the output of this code?
for (int i = 3; i < 3; i++) {
System.out.println("hi");
}
Correct!
Wrong — correct answer is .
The condition 3 < 3 is false before the first iteration.
Q30
Which part of the for header runs only once?
Correct!
Wrong — correct answer is .
The init statement executes once before the loop begins.
Q31
What is the output of this code?
int x = 0;
for (int i = 0; i <= 4; i++) {
x += i;
}
System.out.println(x);
Correct!
Wrong — correct answer is .
The loop adds 0+1+2+3+4 = 10.
Q32
Which is TRUE about the for loop update clause?
Correct!
Wrong — correct answer is .
The update executes at the end of every pass.
Q33
What is the output of this code?
for (char c = 'a'; c <= 'c'; c++) {
System.out.print(c);
}
Correct!
Wrong — correct answer is .
Characters increment through a, b, c.
Q34
What is the output of this code?
for (int i = 1; i <= 5; i += 2) {
System.out.print(i + " ");
}
Correct!
Wrong — correct answer is .
The step of 2 prints 1, 3, 5.
Q35
What happens when you use break in a for loop?
Correct!
Wrong — correct answer is .
break exits the loop and moves to the code after it.
Q36
What is the output of this code?
int total = 0;
for (int i = 1; i <= 4; i++) {
total += i * i;
}
System.out.println(total);
Correct!
Wrong — correct answer is .
Squares 1+4+9+16 = 30.
Q37
Which header loops from 1 to 10 inclusive?
Correct!
Wrong — correct answer is .
Starting at 1 and continuing while i
Q38
What is the output of this code?
for (int i = 0; i < 3; i++)
System.out.print(i);
System.out.print("!");
Correct!
Wrong — correct answer is .
Without braces, only the print(i) is looped; "!" prints once after.