How do I subtract sum of two integers from another integer and then increment it?

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How to subtract sum of x and y from z and then increment it in a single statement in C++

What I have tried:

#include<iostream>
using namespace std;
int main()
{
	int x,y,z,p;
	x=5;
	y=6;
	z=20;
	p=(z-(x+y))++;
	cout<<"value of z="<<p;
}

it's showing error value required as left operand of assignment

Posted 6-Oct-17 5:57am

Member 13074487

Updated 6-Oct-17 6:46am

v2

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David_Wimbley 6-Oct-17 12:12pm

Your issue is likely with x+y=z++;. You probably need to go z=x+y; and then do z++ as z++ is not a variable, ++ is an operator and cannot be treated as part of the variable.

I don't know why you would need to implement in a single statement, seems pretty dumb to me but I guess you could do z = x + y + 1 or z = (x+y)++;. I didn't throw this into a compiler to see if it is valid as I wouldn't try to do a math operation and increment in the same line to begin with, this is probably a homework assignment and not a valid real world situation.

Member 13074487 6-Oct-17 12:16pm

how can I perform all the operation in a single statement? I'm only allowed to use one statement to for calculation

David_Wimbley 6-Oct-17 12:16pm

See revised comment

jeron1 6-Oct-17 12:18pm

'How to subtract sum of x and y from z'
There's no subtraction in your code and
How can this be done if z is uninitialized?

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OriginalGriff · Answer 1 · 2017-10-06T06:46:00

Quote:
I've done this z=z-(x+y); but is it possible to increment it in the same line?????

No. You need what is called an lvalue - because the ++ operator is a "shortcut" operation which basically says "copy this variable, increment it by one, then use the value you remembered". You can only pre-or post fix increment (or decrement) a variable, not an result.

Basically, you are trying to get creative with the auto increment operators: don't. That way lies some really nasty problems. See here: Why does x = ++x + x++ give me the wrong answer?[^]

Jochen Arndt · Answer 2 · 2017-10-06T06:23:00

Solution 1

You need a single variable on the left side of an assignment.

Write the code first in separated statements:

z = z - (x + y); // Subtract sum of x and y from z; or z-= x + y
z = z + 1; // increment z; or z++

Think now how this can be put into one line.
Tip: Subtracting a negative number from a value is equivalent to adding the absolute value of the number.

Posted 6-Oct-17 6:23am

Jochen Arndt

Comments

Member 13074487 6-Oct-17 12:32pm

I've done this z=z-(x+y); but is it possible to increment it in the same line?????

David_Wimbley 6-Oct-17 14:52pm

z=(z-(x+y)) + 1;