Statements and Scope in Java: ISC Class 12 Computer Science

What Statements, Scope is about

Weightage: CISCE publishes no chapter or unit weightage for ISC Computer Science. Statements, Scope is part of Section B, 8 of the 2027 syllabus and can be asked anywhere in the 70-mark Paper 1 (Part I compulsory: ten 1-mark items and a 10-mark short-answer question; Part II: two of three 10-mark questions in each of Sections A and B, and two of three 5-mark questions in Section C).Source: CISCE ISC Computer Science (868) syllabus, examination year 2027; latest Paper 1 specimen (2025) and the 2025 board paper

Key concepts

Conditional statements

1. if: runs a statement or block only when the condition is true.
2. if-else: chooses between two alternatives.
3. if-else-if ladder: tests conditions in order and runs the first true branch; a final else handles all remaining cases.
4. Nested if: an if inside another; an else belongs to the nearest unmatched if (use braces to make the intended pairing clear: the 'dangling else').
5. Ternary operator: condition ? a : b gives a value, so it can be used inside expressions: int big = m > n ? m : n;
6. switch-case: selects a branch by comparing one expression with constant case labels.

• The expression may be int (and byte, short, char), String (Java 7 onwards) or an enum; not long, float, double or boolean.
• Case labels must be distinct constants.
• Without break, execution falls through into the following cases (useful for grouping cases that share code).
• default runs when no case matches; it is optional and can appear anywhere.

switch versus if-else-if: switch tests equality of one expression against constants only; if-else-if can test any conditions, including ranges.

Worked example

[2] State two differences between switch-case and an if-else-if ladder. (Understand)

Try it first, then show the solutionSolution

1. switch tests only equality of one expression with constant values; if-else-if can test any relational or logical conditions, including ranges - 1 mark.
2. switch works with int, char, String (and similar) but not double or boolean; without break it falls through, which does not happen in if-else-if - 1 mark.

Answer: switch compares one expression for equality with constant case labels and works only with int-type, char, String or enum values, falling through without break; an if-else-if ladder can test any conditions (ranges, several variables, doubles) and runs only the first true branch.

Loops, break and continue

1. for (init; condition; update) { body }: best when the number of iterations is known.
2. while (condition) { body }: entry-controlled; the body may run zero times.
3. do { body } while (condition);: exit-controlled; the body runs at least once (note the semicolon).

Infinite loop: a loop whose condition never becomes false (for (;;), while (true), or a missing update).

break: exits the nearest enclosing loop or switch immediately. A labelled break (break outer;) exits the named outer loop.
continue: skips the rest of the current iteration and goes to the next one (in a for loop, the update still runs).

// switch with and without break, break and continue in loops, nested loop with a labelled break.
public class Flow
{
    public static void main(String[] args)
    {
        int code = 2;
        switch (code)             // no break after case 2: falls through to case 3
        {
            case 1:
                System.out.print("one ");
            case 2:
                System.out.print("two ");
            case 3:
                System.out.print("three ");
                break;
            default:
                System.out.print("other ");
        }
        System.out.println();

        for (int i = 1; i <= 10; i++)
        {
            if (i % 3 == 0)
                continue;         // skip multiples of 3
            if (i > 8)
                break;            // stop the loop completely
            System.out.print(i + " ");
        }
        System.out.println();

        outer:
        for (int r = 1; r <= 3; r++)
        {
            for (int c = 1; c <= 3; c++)
            {
                if (r * c == 4)
                    break outer;  // leaves both loops
                System.out.print(r * c + " ");
            }
        }
        System.out.println();

        int n = 0;
        while (n < 3)
            n++;                  // only this statement is in the loop body
        System.out.println("n = " + n);
    }
}

Output:

two three 
1 2 4 5 7 8 
1 2 3 2 
n = 3

Explanation: code 2 prints 'two' and falls through to 'three' until break. The for loop skips 3, 6, 9 with continue and stops at 10 with break. The labelled break leaves both loops as soon as r × c = 4. Without braces, only n++ belongs to the while loop.

Worked example

[2] What is printed by for (int i = 1; i <= 10; i++) { if (i % 3 == 0) continue; if (i > 8) break; System.out.print(i + " "); } ? (Apply)

Try it first, then show the solutionSolution

1. Multiples of 3 (3, 6, 9) are skipped by continue - 1 mark.
2. At i = 10, i > 8 so the loop breaks; output 1 2 4 5 7 8 - 1 mark.

Answer: 1 2 4 5 7 8

Blocks, scope and visibility

A block is a group of statements enclosed in braces { }. A method body, a loop body and an if branch are blocks.

Scope of a variable: the region of the program where it can be used.
1. Local variable: from its declaration to the end of the block in which it is declared. A loop variable declared in a for header exists only inside that loop.
2. Parameter: the whole method body.
3. Instance variable: all instance methods of the class (and other classes, depending on the access modifier).
4. Class (static) variable: all methods of the class, including static ones.

Lifetime: local variables are created when the block is entered and destroyed when it ends; instance variables live as long as their object; static variables live while the class is loaded.

Rules:

• A local variable or parameter with the same name as a field hides (shadows) the field; use this.name to reach the field.
• Two local variables with the same name cannot be in scope at the same time in one method (a block variable cannot redeclare a variable of the enclosing block), but the same name can be reused after the first one's block has ended.

Visibility (access modifiers): private (own class only), default (same package), protected (same package and subclasses), public (everywhere).

// Scope and visibility: instance, static, local and block variables; shadowing.
public class Scope
{
    int value = 10;               // instance variable: visible in all instance methods
    static int shared = 1;        // class variable

    void test(int value)          // the parameter shadows the instance variable
    {
        System.out.println("parameter value = " + value);
        System.out.println("field value     = " + this.value);
        for (int i = 0; i < 2; i++)
        {
            int sq = i * i;       // sq exists only inside this block
            shared += sq;
        }
        // System.out.println(i);  // would not compile: i is out of scope here
        System.out.println("shared = " + shared);
        {
            int temp = 99;        // block-local variable
            System.out.println("temp = " + temp);
        }
        int temp = 5;             // legal: the earlier temp's block has ended
        System.out.println("temp again = " + temp);
    }

    public static void main(String[] args)
    {
        Scope ob = new Scope();
        ob.test(3);
    }
}

Output:

parameter value = 3
field value     = 10
shared = 2
temp = 99
temp again = 5

shared starts at 1 and gains 0 and 1 (squares of i = 0, 1), ending at 2. The second temp is legal because the first one's block had already ended.

Worked example

[2] In the Scope program, why does the line System.out.println(i); after the for loop fail to compile, and what does this.value print? (Analyse)

Try it first, then show the solutionSolution

1. i is declared in the for header, so its scope ends with the loop; it cannot be used afterwards - 1 mark.
2. The parameter value (3) shadows the field; this.value refers to the instance variable, which is 10 - 1 mark.

Answer: i is out of scope after the loop, so the compiler rejects the line; this.value prints the field's value 10, while value alone gives the parameter 3.

Tracing and completing code with conditions and loops

Question 2 often gives a method with blanks. Strategy:
1. Read the comment or description: what should the method return?
2. Identify each variable's role (counter, accumulator, flag, minimum, current digit).
3. Fill blanks so that the loop starts, continues and stops correctly, and so that the flag or accumulator has a sensible starting value.
4. Test with one or two values by tracing.

Example: a Spy number has equal sum and product of digits (1124: 1 + 1 + 2 + 4 = 8 and 1 × 1 × 2 × 4 = 8).

boolean isSpy(int n)
{
    int sum = 0, prod = 1;
    for (int t = n; t > 0; t = t / 10)
    {
        int d = t % 10;
        sum = sum + d;
        prod = prod * d;
    }
    return sum == prod;
}

Key choices: prod starts at 1 (0 would make every product 0); the update t = t / 10 changes the loop variable itself; the test uses ==. isSpy(1124) and isSpy(123) are both true (for 123: 1 + 2 + 3 = 6 = 1 × 2 × 3), while isSpy(124) is false (sum 7, product 8).

Worked example

[3] In isSpy above, the lines are replaced by ?1? for the initial value of prod, ?2? for the loop update and ?3? for the return expression. State them and give isSpy(124). (Apply)

Try it first, then show the solutionSolution

1. ?1? = 1 (the identity for multiplication) - 1 mark.
2. ?2? = t = t / 10 (or t /= 10) - 1 mark.
3. ?3? = sum == prod; for 124: sum 7, product 8, so false - 1 mark.

Answer: ?1? = 1; ?2? = t = t / 10; ?3? = sum == prod. isSpy(124) returns false (7 ≠ 8).

A complete program with switch, loops and validation

Converting a day number of a year into a date uses an if for validation, a switch with grouped cases for month lengths, a while loop to subtract months, and a leap-year test:
leap year: divisible by 4 and not by 100, or divisible by 400.

import java.util.Scanner;

// Converts a day number (1-365 or 1-366) of a given year into a date.
public class DayToDate
{
    int day, year;

    DayToDate()
    {
        day = 0;
        year = 0;
    }

    void accept()
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter day number and year:");
        day = sc.nextInt();
        year = sc.nextInt();
    }

    boolean isLeap(int y)
    {
        return (y % 4 == 0 && y % 100 != 0) || y % 400 == 0;
    }

    int daysIn(int m)
    {
        switch (m)
        {
            case 2:
                return isLeap(year) ? 29 : 28;
            case 4:
            case 6:
            case 9:
            case 11:
                return 30;        // grouped cases share one statement
            default:
                return 31;
        }
    }

    String monthName(int m)
    {
        String name;
        switch (m)
        {
            case 1: name = "January"; break;
            case 2: name = "February"; break;
            case 3: name = "March"; break;
            case 4: name = "April"; break;
            case 5: name = "May"; break;
            case 6: name = "June"; break;
            case 7: name = "July"; break;
            case 8: name = "August"; break;
            case 9: name = "September"; break;
            case 10: name = "October"; break;
            case 11: name = "November"; break;
            default: name = "December";
        }
        return name;
    }

    void convert()
    {
        int limit = isLeap(year) ? 366 : 365;
        if (day < 1 || day > limit)
        {
            System.out.println("Invalid day number");
            return;
        }
        int m = 1, d = day;
        while (d > daysIn(m))
        {
            d = d - daysIn(m);
            m++;
        }
        System.out.println("Day " + day + " of " + year + " is " + d + " " + monthName(m) + " " + year);
    }

    public static void main(String[] args)
    {
        DayToDate ob = new DayToDate();
        ob.accept();
        ob.convert();
    }
}

Input: 255 2024

Enter day number and year:
Day 255 of 2024 is 11 September 2024

Other runs: 255 2025 → 12 September 2025 (non-leap year, so one day later); 60 2024 → 29 February 2024; 366 2023 → Invalid day number; 365 2026 → 31 December 2026.

The switch in daysIn( ) groups cases 4, 6, 9 and 11 by letting them fall through to one return statement; monthName( ) uses break after each case.

Worked example

[2] Trace convert( ) for day 60 of 2024 and give the output. (Apply)

Try it first, then show the solutionSolution

1. d = 60 > 31 (January) → d = 29, m = 2 - 1 mark.
2. 2024 is a leap year, so February has 29 days; 29 > 29 is false, loop stops: 29 February 2024 - 1 mark.

Answer: Day 60 of 2024 is 29 February 2024.

Statements, 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 and Looping Statements, Blocks and Variable Scope

Statements, Scope: syntax and key facts

Leap year

(y % 4 == 0 && y % 100 != 0) || y % 400 == 0

2024 leap; 1900 not; 2000 leap.

switch types

int, short, byte, char, String, enum (not long, float, double, boolean)

Case labels: distinct constants.

Loop types

for (known count); while (0 or more); do-while (1 or more)

do-while ends with ;

break / continue

break: exit loop or switch; continue: next iteration

Labelled break exits an outer loop.

Scope

Local: declaration to end of its block; field: whole class

this.x reaches a shadowed field.

How the board asks Statements, Scope

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

Tricks to remember Statements, Scope

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

• Ternary as a mini if

  cond ? yes : no.

  Use it when: Reading and writing ?:.

• Leap rule 4-100-400

  Every 4, except every 100, except every 400.

  Use it when: Leap-year test.

• Braces decide

  No braces: only the next single statement belongs to the if or loop.

  Use it when: Tracing indentation traps.

Statements, Scope: board-level solved questions

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

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 6-mark question split into 2 + 2 + 1 + 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, Scope

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

• ✗Mistake: Wrong starting value in a minimum or product

  CISCE examiners' comments, 2024: in a smallest-digit method candidates 'Took initial min as 0 or -1' and 'Did not realise remainder is obtained as n - q*10 in this code'.

  ✓Do this: Start a minimum at 9 (or the number itself) and a product at 1; recognise that n - (n / 10) × 10 is the same as n % 10.

  Usually costs: 1 mark per blank.

• ✗Mistake: Loop update that does not change the loop variable

  CISCE examiners' comments, 2025: in the duck-number method candidates 'Wrote i = a/10 or only i/10 instead of i = i/10 for ?1?' and 'Gave vague answers for ?2?'.

  ✓Do this: The update must reassign the loop variable from itself: i = i / 10. Give exact values (0, -1) in blanks, not descriptions.

  Usually costs: 1 mark per blank.

• ✗Mistake: Confusing break in loops with break in switch

  CISCE examiners' comments, 2025: on break and fall-through, candidates 'Confused between options A and B because of the word loop in the Reason'.

  ✓Do this: break exits whichever loop or switch encloses it; in a switch that is what prevents fall-through.

  Usually costs: 1 mark.

• ✗Mistake: Using a variable outside its scope

  A for-loop variable or a block variable cannot be used after its block; such answers do not compile.

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

  Usually costs: 1 mark.

Practice questions on Statements, 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 · Very short answerBoard level

   What is the output of int a = 9; System.out.println(a % 2 == 0 ? "even" : "odd");?

   Hint

   9 % 2.

   Answer

   odd

2. Q2 · 1 mark · Very short answerBoard level

   Is 1900 a leap year?

   Hint

   Century rule.

   Answer

   No: it is divisible by 100 but not by 400.

3. Q3 · 1 mark · Very short answerBoard level

   What does continue do in a for loop?

   Hint

   Skips the rest.

   Answer

   It skips the remaining statements of the current iteration, runs the update and goes to the next iteration.

4. Q4 · 1 mark · Very short answerHarder board level

   Give the output: int s = 0; for (int i = 5; i > 0; i -= 2) s += i; System.out.println(s);

   Hint

   5, 3, 1.

   Answer

   9

5. Q5 · 2 marks · Short answerHarder board level

   [2] Rewrite using a while loop: for (int i = 10; i >= 1; i -= 3) System.out.print(i + " "); and give the output.

   Hint

   Initialise before, update inside.

   Answer

   int i = 10; while (i >= 1) { System.out.print(i + " "); i -= 3; } Output: 10 7 4 1

6. Q6 · 3 marks · Short answerHarder board level

   [3] Fill the blanks so that the method returns true if n contains the digit 7: boolean hasSeven(int n) { boolean f = ?1?; while (n > 0) { if (?2?) { f = true; break; } ?3?; } return f; }

   Hint

   Flag starts false.

   Answer

   ?1? = false; ?2? = n % 10 == 7; ?3? = n = n / 10. hasSeven(1729) is true and hasSeven(1234) is false.

7. Q7 · 5 marks · Long answerHOTS / competency

   [5] Write a method that prints all numbers from 1 to 100 that are divisible by 3 or 5 but not by both, using continue to skip numbers divisible by both, and state how many it prints.

   Hint

   Multiples of 15 are skipped.

   Answer

   for (int i = 1; i <= 100; i++) { if (i % 15 == 0) continue; if (i % 3 == 0 || i % 5 == 0) System.out.print(i + " "); } It prints 41 numbers (33 multiples of 3 + 20 multiples of 5 - 2 × 6 multiples of 15), checked by running the code.

8. Q8 · 10 marks · Long answerHOTS / competency

   [10] Design a class Grade with data members name and an array of five marks; a constructor; void accept( ); double average( ); char grade( ) using an if-else-if ladder (A: 90 and above, B: 75-89, C: 60-74, D: 40-59, E: below 40) applied to the average; and void report( ). Write main( ).

   Hint

   Test from the highest band down.

   Answer

   Constructor initialises name = "" and the array; accept( ) reads the name and five marks; average( ) returns the sum / 5.0; grade( ): if avg >= 90 'A' else if avg >= 75 'B' else if avg >= 60 'C' else if avg >= 40 'D' else 'E'; report( ) prints name, average and grade; main( ) calls accept( ) and report( ). For marks 78, 85, 91, 66, 70 the average is 78.0 and the grade B (checked by running the code).

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.Which loop is exit-controlled?Show answer

   do-while.

2. 2.What happens without break in a switch case?Show answer

   Execution falls through to the next case.

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

   Only inside that loop.

4. 4.How do you reach a field hidden by a parameter?Show answer

   this.fieldName.

5. 5.Day 255 of 2024?Show answer

   11 September 2024.

Quick revision checklist

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

• ☐if-else-if: first true branch runs; else pairs with the nearest if.
• ☐switch: int, char, String, enum; break stops fall-through; default optional.
• ☐for (count known), while (may be 0), do-while (at least 1).
• ☐break exits; continue skips to next iteration.
• ☐Scope: local to its block; fields to the class; this.x for shadowed fields.
• ☐Leap year: (y % 4 == 0 && y % 100 != 0) || y % 400 == 0.

Statements, Scope: frequently asked questions