explain working of post and pre increment operator in Java

Question

can you explain me the output of this in case of Java

int a=5,i;

i=++a + ++a + a++;
i=a++ + ++a + ++a;

a=++a + ++a + a++;

System.out.println(a);

System.out.println(i);

The output is 20 in both cases

Answer 1

++a increments a before it is evaluated. a++ evaluates a and then increments it.

Answer 2

i=++a + ++a + a++;

is

i = 6 + 7 + 7

Working: increment a to 6 (current value 6) + increment a to 7 (current value 7). Sum is 13 now add it to current value of a (=7) and then increment a to 8. Sum is 20 and value of a after the assignment completes is 8.

i=a++ + ++a + ++a;

is

i=5 + 7 + 8

Working: At the start value of a is 5. Use it in the addition and then increment it to 6 (current value 6). Increment a from current value 6 to 7 to get other operand of +. Sum is 12 and current value of a is 7. Next increment a from 7 to 8 (current value = 8) and add it to previous sum 12 to get 20.

Answer 3

Does this help?

i=++a + ++a + a++; =>
i=6 + 7 + 7; (a=8)

i=a++ + ++a + ++a; =>
i=5 + 7 + 8; (a=8)

Answer 4

when a is 5, then a++ gives a 5 to the expression, and ++a gives a 6 to the expression.

So you calculate

i = 6 + 7 + 7
i = 5 + 7 + 8

Answer 5

++a increments and then uses the variable a++ uses and then increments the variable

if you have

a = 1

and you do

System.out.println(a++) //you will see 1

//Now a is 2

System.out.println(++a) //you will see 3

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