Statements and Scope in Java: ISC Class 11 Notes

What Statements and Scope is about

Weightage: Statements and Scope is topic 8 of the ISC Class XI Computer Science syllabus, in Section B - Java. CISCE weights Section B at 30 of the 70 marks in Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Computer Science syllabus, examination year 2028, Class XI unit weightage

Key concepts

Statements and blocks

A statement is a complete instruction. Kinds:

1. Declaration statements: int n = 5;
2. Expression statements: assignments, increments, method calls: n++; System.out.println(n);
3. Control statements: conditionals (if, switch), loops (for, while, do-while), jumps (break, continue, return).

A block (compound statement) is a group of statements enclosed in braces { }; it can appear wherever a single statement can. Blocks are needed when an if or a loop must control more than one statement:

if (marks >= 40)
{
    passed++;
    System.out.println("Pass");
}

Without braces, only the first statement belongs to the if; the second always runs. Nesting: blocks can contain other blocks (a loop inside an if inside a method).

Empty statement: a lone semicolon. Beware: for (i = 0; i < 5; i++); { ... } runs an empty loop five times, then the block once.

Worked example

What is printed by: int c = 0; for (int i = 1; i <= 3; i++); c++; System.out.println(c);? [1 mark]

Try it first, then show the solutionSolution

1. The semicolon after the for header makes the loop body empty; c++ runs once after the loop.

Answer: 1.

Conditional statements: if, if-else, if-else-if

if: runs a statement (or block) only when the condition is true.

if-else: chooses between two alternatives.

if-else-if ladder: tests conditions in order; the first true condition's block runs and the rest are skipped; a final else handles all remaining cases.

Nested if: an if inside another if. Dangling else rule: an else belongs to the nearest unmatched if; use braces to make the intent clear.

Evaluation of conditions: the condition must be a boolean expression (Java does not treat 0 as false). && and || short-circuit.

The grade method below uses an if-else-if ladder; because conditions are tested from the top, marks ≥ 75 need not also test < 90.

// if, if-else, if-else-if ladder, switch (with and without break) and the ternary operator.
public class Conditionals
{
    static char grade(int marks)
    {
        if (marks >= 90)
            return 'A';
        else if (marks >= 75)
            return 'B';
        else if (marks >= 60)
            return 'C';
        else if (marks >= 40)
            return 'D';
        else
            return 'E';
    }

    static String dayName(int d)
    {
        String name;
        switch (d)
        {
            case 1: name = "Monday"; break;
            case 2: name = "Tuesday"; break;
            case 6:
            case 7: name = "Weekend"; break;        // two cases share one block
            default: name = "Midweek";
        }
        return name;
    }

    public static void main(String[] args)
    {
        int[] marks = {95, 75, 61, 40, 12};
        for (int i = 0; i < marks.length; i++)
            System.out.print(marks[i] + ":" + grade(marks[i]) + " ");
        System.out.println();

        System.out.println(dayName(1) + ", " + dayName(4) + ", " + dayName(7));

        int k = 2;
        switch (k)                              // missing break: fall-through
        {
            case 1: System.out.print("one ");
            case 2: System.out.print("two ");
            case 3: System.out.print("three ");
            default: System.out.print("default");
        }
        System.out.println();

        int a = 14, b = 9;
        int bigger = (a > b) ? a : b;           // ternary operator
        String parity = (a % 2 == 0) ? "even" : "odd";
        System.out.println("bigger = " + bigger + ", " + a + " is " + parity);
    }
}

Output:

95:A 75:B 61:C 40:D 12:E 
Monday, Midweek, Weekend
two three default
bigger = 14, 14 is even

Worked example

Using grade(), which grade is returned for 74 and for 90, and why does the order of conditions matter? [2 marks]

Try it first, then show the solutionSolution

1. 74: fails ≥ 90 and ≥ 75, passes ≥ 60 → 'C'. 90: passes the first test → 'A'.
2. If marks >= 60 were tested first, 90 would wrongly get 'C': in a ladder the first true branch wins.

Answer: 74 → C, 90 → A; conditions must go from the strictest to the weakest.

switch-case and the ternary operator

switch selects one of many branches by matching an expression against constant case labels.

• The expression may be int, char, short, byte, String (or an enum or a wrapper of these) but not double, float, long or boolean.
• Case labels must be constants and distinct.
• break ends the switch; without it, execution falls through into the next case (useful when several cases share code, as with cases 6 and 7 above).
• default runs when no case matches; it is optional.

In the program above, k = 2 with no breaks printed 'two three default': execution entered at case 2 and fell through every following case.

if-else-if vs switch: switch tests only equality with constants; if-else-if can test ranges and any boolean condition.

Ternary (conditional) operator ?: is an expression that chooses one of two values:

condition ? valueIfTrue : valueIfFalse

int bigger = (a > b) ? a : b;. It can be nested (right-associative), but deep nesting harms readability.

Worked example

Rewrite with the ternary operator: if (n % 2 == 0) s = "even"; else s = "odd";. [1 mark]

Try it first, then show the solutionSolution

1. Assign the result of the conditional expression.

Answer: s = (n % 2 == 0) ? "even" : "odd";

Loops: for, while, do-while

for: for (initialisation; condition; update) body. Best when the number of repetitions is known. The condition is tested before each iteration.

while: while (condition) body. Entry-controlled: the condition is tested first, so the body may run zero times. Best when repetitions depend on a condition (for example, until a number becomes 0).

do-while: do body while (condition);. Exit-controlled: the body runs at least once, then the condition is tested. Note the semicolon after while (condition).

Parts of a loop: initialisation, test condition, body, update. Forgetting the update (or a wrong condition) gives an infinite loop.

Counting iterations: for (i = 10; i > 0; i −= 3) runs for i = 10, 7, 4, 1: 4 times.

// for, while and do-while loops, with break and continue.
public class Loops
{
    public static void main(String[] args)
    {
        // for: a known number of repetitions
        int sum = 0;
        for (int i = 1; i <= 10; i++)
            sum += i;
        System.out.println("1 + 2 + ... + 10 = " + sum);

        // while: repeat while a condition holds (count the digits)
        int n = 90817, digits = 0;
        while (n > 0)
        {
            digits++;
            n /= 10;
        }
        System.out.println("digits in 90817 = " + digits);

        // do-while: body runs at least once
        int x = 50;
        do
        {
            System.out.println("do-while body ran with x = " + x);
            x++;
        } while (x < 10);

        // continue: skip multiples of 3
        System.out.print("1 to 10 without multiples of 3: ");
        for (int i = 1; i <= 10; i++)
        {
            if (i % 3 == 0)
                continue;
            System.out.print(i + " ");
        }
        System.out.println();

        // break: first number above 100 divisible by both 7 and 9
        int found = 0;
        for (int i = 101; ; i++)
        {
            if (i % 7 == 0 && i % 9 == 0)
            {
                found = i;
                break;
            }
        }
        System.out.println("first above 100 divisible by 7 and 9 = " + found);

        // nested loops: a number triangle
        for (int row = 1; row <= 4; row++)
        {
            for (int col = 1; col <= row; col++)
                System.out.print(col);
            System.out.println();
        }
    }
}

Output:

1 + 2 + ... + 10 = 55
digits in 90817 = 5
do-while body ran with x = 50
1 to 10 without multiples of 3: 1 2 4 5 7 8 10 
first above 100 divisible by 7 and 9 = 126
1
12
123
1234

Note that the do-while body ran once even though x = 50 already failed x < 10.

Worked example

How many times does the body run, and what is i afterwards: int i = 1; while (i < 50) i *= 3;? [2 marks]

Try it first, then show the solutionSolution

1. i: 1 → 3 → 9 → 27 → 81; the test fails at 81.
2. Body ran 4 times.

Answer: 4 times; i = 81.

break and continue; nested loops

break: immediately exits the innermost loop (or switch); control passes to the statement after it. Used to stop a search once the answer is found.

continue: skips the rest of the current iteration and goes to the next one (in a for loop, the update runs first). Used to skip unwanted values.

Nested loops: a loop inside a loop; the inner loop runs completely for each iteration of the outer loop. Patterns, tables and pairs are typical uses: an outer loop of 4 rows and an inner loop of row columns prints a number triangle (as in the Loops program).

break inside an inner loop exits only the inner loop.

Example of break and continue together: summing odd numbers up to 15 from a loop running to 20: for (k = 1; k <= 20; k++) { if (k % 2 == 0) continue; if (k > 15) break; sum += k; } gives 1 + 3 + ... + 15 = 64.

Worked example

In the Loops program, why is the first number found 126? [1 mark]

Try it first, then show the solutionSolution

1. Divisible by both 7 and 9 means divisible by 63; multiples are 63, 126, ...; the first above 100 is 126, and break stops the search.

Answer: 126 = 2 × 63 is the first multiple of 63 above 100; break ends the loop there.

Scope and visibility of variables

The scope of a variable is the part of the program where it can be used.

1. Class scope: instance and static variables (fields) declared in a class are visible in all methods of the class.
2. Method scope: parameters and local variables declared in a method are visible from the declaration to the end of the method; they are created when the method is called and destroyed when it returns.
3. Block scope: a variable declared inside a block (including a for-loop header) is visible only inside that block.

Visibility rules for the same name:

• A local variable or parameter with the same name as a field hides (shadows) the field inside that method; the field is still reached with this.name.
• Two local variables with the same name cannot be declared where their scopes overlap (a block inside a method cannot redeclare the method's local variable), but the same name can be reused after an earlier block has ended.

// Class scope, method scope and block scope; a local variable hiding a field of the same name.
public class Scope
{
    int count = 100;                   // class scope (instance variable)

    void show()
    {
        int count = 5;                 // method scope: hides the field inside this method
        System.out.println("local count = " + count + ", field count = " + this.count);
        for (int i = 0; i < 2; i++)    // i exists only inside the loop
        {
            int sq = i * i;            // block scope: sq exists only in this block
            System.out.println("i = " + i + ", sq = " + sq);
        }
        // System.out.println(i);      // would not compile: i is out of scope here
    }

    void increase()
    {
        count++;                       // no local count here, so this is the field
    }

    public static void main(String[] args)
    {
        Scope s = new Scope();
        s.show();
        s.increase();
        System.out.println("after increase, field count = " + s.count);
        {
            int temp = 7;              // a block inside main
            System.out.println("temp in block = " + temp);
        }
        int temp = 8;                  // allowed: the earlier temp is out of scope
        System.out.println("temp after block = " + temp);
    }
}

Output:

local count = 5, field count = 100
i = 0, sq = 0
i = 1, sq = 1
after increase, field count = 101
temp in block = 7
temp after block = 8

Worked example

Why can main declare int temp = 8; after a block that declared int temp = 7;? [1 mark]

Try it first, then show the solutionSolution

1. The first temp has block scope; it ceases to exist at the closing brace, so the name is free again.

Answer: Because the earlier temp's scope ended with its block; the scopes do not overlap.

Statements and Scope in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Conditional Statements in Java: if, if-else-if, switch and the Ternary Operator
• Loops in Java: for, while, do-while, break, continue, Nested Loops and Scope

Statements and Scope: syntax and key facts

Iterations of a counting loop

for (i = a; i <= b; i += s): number of iterations = floor((b − a) ÷ s) + 1 (if a ≤ b)

Ternary operator

result = condition ? valueIfTrue : valueIfFalse;

switch skeleton

switch (expr) { case c1: ... break; case c2: ... break; default: ... }

Loop types

for and while: entry-controlled (0 or more runs); do-while: exit-controlled (1 or more runs)

Scope order

Class scope ⊃ method scope ⊃ block scope; inner name hides outer; this.name reaches the field

Statements and Scope: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Statements and Scope

The question patterns to expect, and the method that works for each.

Tricks to remember Statements and Scope

Short memory aids. Say each one aloud once, then use it on a question the same day.

• for = know how many; while = know when to stop; do-while = at least once

  Pick the loop by what you know before starting.

  Use it when: Choosing a loop.

• No break, fall through

  Every case without break slides into the next.

  Use it when: switch behaviour.

• break leaves, continue skips

  break exits the loop; continue jumps to the next turn.

  Use it when: Jump statements.

• Braces are borders

  A variable lives only inside the braces where it was born.

  Use it when: Block scope.

Statements and Scope: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

// Prints all three-digit Armstrong numbers (sum of cubes of digits equals the number)
// and counts them, using nested loops and a while loop.
public class Armstrong
{
    public static void main(String[] args)
    {
        int count = 0;
        for (int n = 100; n <= 999; n++)
        {
            int t = n, s = 0;
            while (t > 0)
            {
                int d = t % 10;
                s += d * d * d;
                t /= 10;
            }
            if (s == n)
            {
                System.out.print(n + " ");
                count++;
            }
        }
        System.out.println();
        System.out.println("count = " + count);
    }
}

153 370 371 407 
count = 4

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 2 + 2 + 1 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Statements and Scope

The slips examiners see most often, and what to write instead.

• ✗Mistake: Forgetting break in switch

  Execution falls through into the following cases.

  ✓Do this: End each case with break unless fall-through is intended.

  Usually costs: 1-2 marks.

• ✗Mistake: Semicolon after a for or while header

  It makes an empty loop body; the intended body runs once afterwards.

  ✓Do this: No semicolon before the body's opening brace.

  Usually costs: 1-2 marks.

• ✗Mistake: Using a loop variable after the loop when it was declared in the for header

  Its scope is only the loop.

  ✓Do this: Declare it before the loop if needed afterwards.

  Usually costs: 1 mark.

• ✗Mistake: Destroying the original number in digit loops

  After the loop the number is 0, so it cannot be compared or printed.

  ✓Do this: Work on a copy.

  Usually costs: 1 mark.

Practice questions on Statements and Scope

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Which loop is exit-controlled?
   (a) for
   (b) while
   (c) do-while
   (d) all of these

   Hint

   Test after the body.

   Answer

   (c) do-while.

2. Q2 · 1 mark · Very short answerExam level

   How many times does for (int i = 10; i > 0; i -= 3) run?

   Hint

   List the values.

   Answer

   4 times (i = 10, 7, 4, 1).

3. Q3 · 2 marks · Short answerExam level

   Distinguish between break and continue with an example each.

   Hint

   Exit vs skip.

   Answer

   break exits the loop immediately (stop searching once a number is found). continue skips the rest of the current iteration and moves to the next (skip multiples of 3 while printing 1 to 10).

4. Q4 · 2 marks · Short answerHarder exam level

   Write a switch that prints 'vowel' or 'consonant' for a lower-case letter ch, using fall-through.

   Hint

   Stack the vowel cases.

   Answer

   switch (ch) { case 'a': case 'e': case 'i': case 'o': case 'u': System.out.println("vowel"); break; default: System.out.println("consonant"); } For ch = 'e' it prints vowel.

5. Q5 · 2 marks · Short answerHarder exam level

   What is y after int x = 5; int y = x > 3 ? x < 8 ? 1 : 2 : 3;? Explain the grouping.

   Hint

   Right-associative.

   Answer

   It groups as x > 3 ? (x < 8 ? 1 : 2) : 3. x > 3 is true, x < 8 is true, so y = 1.

6. Q6 · 2 marks · Short answerHarder exam level

   Write a loop to print the first 8 Fibonacci numbers starting 0, 1.

   Hint

   Keep two previous terms.

   Answer

   int a = 0, b = 1; for (int k = 1; k <= 8; k++) { System.out.print(a + " "); int c = a + b; a = b; b = c; } Output: 0 1 1 2 3 5 8 13.

7. Q7 · 2 marks · Short answerHOTS / competency

   Identify the scope error and correct it: for (int i = 0; i < 5; i++) { int sq = i * i; } System.out.println(i + " " + sq);

   Hint

   Block scope.

   Answer

   i (declared in the for header) and sq (declared in the block) are out of scope after the loop, so the println does not compile. Declare int i, sq; before the loop (or print inside the loop). After the corrected loop ends, i = 5 and sq = 16.

8. Q8 · 5 marks · Short answerHarder exam level

   Write a program segment that checks whether 28 is a perfect number (equal to the sum of its proper divisors) and prints the result.

   Hint

   Divisors less than n.

   Answer

   int n = 28, s = 0; for (int d = 1; d < n; d++) if (n % d == 0) s += d; System.out.println(n + " perfect? " + (s == n)); Divisors 1, 2, 4, 7, 14 sum to 28, so it prints true.

9. Q9 · 2 marks · Short answerHOTS / competency

   Trace and give the output: int m = 5; do { m -= 2; } while (m > 0); System.out.println(m);

   Hint

   Test after each subtraction.

   Answer

   m: 5 → 3 (test true) → 1 (true) → −1 (false); prints −1.

10. Q10 · 10 marks · Long answerHOTS / competency

    Write a program to find the GCD of two numbers using a while loop (Euclid's method) and the LCM from it, and give the result for 48 and 36.

    Hint

    gcd(a, b) = gcd(b, a % b); LCM = a × b ÷ GCD.

    Answer

    int a = 48, b = 36, x = a, y = b; while (y != 0) { int t = x % y; x = y; y = t; } int gcd = x; int lcm = a * b / gcd; Trace: (48, 36) → (36, 12) → (12, 0): GCD = 12; LCM = 48 × 36 ÷ 12 = 144. The while loop suits because the number of steps is not known in advance.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Entry-controlled loops?Show answer

   for and while.

2. 2.What does break do in a switch?Show answer

   Ends the switch, preventing fall-through.

3. 3.Ternary operator form?Show answer

   condition ? a : b.

4. 4.Scope of a for-loop variable?Show answer

   Only the loop.

5. 5.Local variable with a field's name?Show answer

   Hides the field; use this.name for the field.

6. 6.continue does?Show answer

   Skips to the next iteration.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Block = { } groups statements; without braces only one statement is controlled.
• ☐if-else-if: first true branch wins; dangling else pairs with nearest if.
• ☐switch: constant cases, break to stop fall-through, default optional; no double or boolean.
• ☐for/while test first; do-while tests after (runs at least once).
• ☐break exits; continue skips; inner loop completes for each outer iteration.
• ☐Scope: class ⊃ method ⊃ block; inner name hides outer; this.field.

Statements and Scope: frequently asked questions