Increment, Decrement, Shorthand Operators and Precedence in Java (ICSE Class 10)

Understand Increment, Decrement, Shorthand Operators and Precedence

Increment, Decrement, Shorthand Operators and Precedence: key facts

Prefix and postfix

• •++x: change, then use
• •x++: use, then change
• •Used alone, both add 1

The same for --.

Shorthand assignment

• •x += y means x = x + y
• •x -= y means x = x - y
• •x /= y means x = x / y
• •x %= y means x = x % y
• •the whole right side is solved first

The whole right side is calculated first.

Precedence order

• •postfix
• •prefix and unary
• •multiply, divide, remainder
• •add, subtract
• •< > <= >=
• •== !=
• •&&
• •||
• •?:
• •assignment

Brackets override everything.

Associativity

Binary operators of one level	left to right
Assignment	right to left
Unary	right to left

12 / 4 * 3 = 9.

How to answer Increment, Decrement, Shorthand Operators and Precedence questions

1. 1Write the starting value of every variable.
2. 2Rewrite the expression with brackets showing the precedence order.
3. 3Move left to right through each level; for x++ take the old value and then update x, for ++x update x and then take the value.
4. 4After each statement write the new value of every variable that changed.
5. 5For a printing statement, evaluate each part in order; an int joined to a string with + becomes text.

Increment, Decrement, Shorthand Operators and Precedence in real life

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

Tricks to remember Increment, Decrement, Shorthand Operators and Precedence

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

• Prefix = Preview first

  ++x changes before you see it; x++ shows the old value and then changes.

  Use it when: Pre vs post questions.

• PEMDAS-like ladder

  Unary, then * / %, then + -, then comparisons, then &&, then ||, then ?:, then =.

  Use it when: Long expressions.

• Equals goes last

  The assignment sign is the lowest, so the whole right side is solved before storing.

  Use it when: Shorthand operators such as x *= 3 + 2.

Increment, Decrement, Shorthand Operators and Precedence: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

int x = 5;
int y = x++ + ++x;
System.out.println(x + " " + y);

int a = 4, b = 3;
a += b++ * 2;
b -= --a;
System.out.println(a + " " + b);

int r = 10 + 4 * 3 % 5 - 2;
int p = 5;
boolean q = p > 3 && p < 10 || p == 0;
System.out.println(r + " " + q);

int c = 0, t = 0;
for (int i = 1; i <= 5; i++) {
    if (i % 2 == 0)
        c++;
    else
        t += i;
}
System.out.println(c + " " + t);

int m = 72, a = 8, b = 12;
String g = m >= 90 ? "A" : m >= 75 ? "B" : m >= 60 ? "C" : "D";
int big = a > b ? a : b;
System.out.println(g + " " + big);

Where students lose marks in Increment, Decrement, Shorthand Operators and Precedence

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

• ✗Mistake: Using the new value for a postfix

  In y = x++, y receives the old value; x is increased afterwards.

  Wrong working

  x = 5; y = x++; y = 6

  Right working

  x = 5; y = x++; y = 5, x = 6

  ✓Do this: Write "use, then change" next to x++.

  Usually costs: 1 mark

• ✗Mistake: Doing + before * in an expression

  * / % have higher precedence than + -.

  Wrong working

  10 + 4 * 3 = 42

  Right working

  10 + 4 * 3 = 22

  ✓Do this: Draw brackets round * / % first.

  Usually costs: 1 mark

• ✗Mistake: Misreading shorthand with a bracket-less right side

  x *= 3 + 2 means x = x * (3 + 2), not (x * 3) + 2.

  Wrong working

  x = 5; x *= 3 + 2; x = 17

  Right working

  x = 5; x *= 3 + 2; x = 25

  ✓Do this: Replace the shorthand by the full form with brackets.

  Usually costs: 1 mark

Practice questions on Increment, Decrement, Shorthand Operators and Precedence

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 · MCQBoard level

   What is the value of the expression 10 + 3 * 2?
   (a) 26 (b) 16 (c) 19 (d) 12

   Hint

   • comes before +.

   Answer

   (b) 16

2. Q2 · 1 mark · Very short answerBoard level

   What is the value of x after:
   int x = 5; x *= 3 + 2;

   Hint

   Solve the right side first.

   Answer

   25, since x = x * (3 + 2) = 5 * 5.

3. Q3 · 2 marks · Short answerHarder board level

   Find the output:

   int a = 3;
   int b = a++ * 2 + a;
   System.out.println(a + " " + b);

   Hint

   a changes after its old value is used.

   Answer

   4 10 (a++ gives 3 and a becomes 4; b = 3 * 2 + 4 = 10)

4. Q4 · 2 marks · Short answerHarder board level

   Write the output:

   int k = 7;
   System.out.println(k++ + " " + k + " " + --k);

   Hint

   Evaluate the three parts from left to right.

   Answer

   7 8 7 (k++ gives 7 then k is 8; k gives 8; --k makes k 7 and gives 7)

5. Q5 · 1 mark · Assertion-reasonHOTS / competency

   Assertion (A): For the statements x++; and ++x; written alone, the final value of x is the same.
   Reason (R): The difference between prefix and postfix is seen only when the value of the expression is used.
   (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.

   Hint

   Is the value of the expression used when written alone?

   Answer

   (a) Both are true and R explains A.

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.What does y = x++ do?Show answer

   Stores the old value of x in y, then increases x by 1.

2. 2.What does x += 5 mean?Show answer

   x = x + 5

3. 3.Name the only ternary operator.Show answer

   ?:

4. 4.Which has higher precedence: % or +?Show answer

   %

5. 5.Give the associativity of the assignment operator.Show answer

   Right to left.

6. 6.Are bitwise operators in the Class X syllabus?Show answer

   No.

Increment, Decrement, Shorthand Operators and Precedence: frequently asked questions