Question

The Following Java expression:

S/10 * 10 + 10 – S = C

Show that this expression gives a value of 2 when S contains the int value 78. You must show every step in your working, performing exactly one operation on each line.

I have tried to no end to make sense of this and I know there is an order of precedence in the operators but I can't make any sense of it. Could someone please explain this to me?

Answer 1

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Answer =>
The operator precedence is as follows:
* / %    Multiplication, Division,    Modulo    Left-to-right means whichever comes in the left will get higher precedence.
+ -      addition,       subtraction            Left-to-right

So the expression S/10 * 10 + 10 – S = C  will be performed by Java as follows

Step 01. => Replace variables with the original value (S =78). So expression becomes.
            78/10 * 10 + 10 – 78

Step 02. => 78/10 will be done first and decimal will be truncated. Division and multiplication have the highest precedence than addition and subtraction. 
            Here the division (/) will have the highest precedence over multiplication (*) since division is on the left side of the expression. 
            so the division operator will execute first.
            78/10 = 7.8 truncated to 7 and expression will be like 
            7*10 + 10 -78   

Step 03. => 7*10 will be executed as multiplication (*) is precedence over the other operators (+ and -) and expression will become
            70 + 10 -78

Step 04. => 70 + 10 will be executed as operator addition (+) is on the left-hand side and will have higher precedence. And the expression will become
            80 -78

Step 05. => last the minus (-) operator will be executed and the result will become 2.

Why the java is giving 78/10 as 7 in Step 02., is because the S is an integer. The illustration is given below.

Output