Addition and subtraction using increment and decrement operators. C++

Question

I have been given a task to add and subtract two int variables WITHOUT using the built in operators (+ and -) and instead using the increment and decrement operators. How do I go about doing this?

    int add1;
    int add2; 
    int total;

    cout << "Please enter the 2 numbers you wish to add" << endl;
    cin >> add1;
    cin >> add2;

    //perform addition using increment operators

    return 0;

thanks for the help!

Is it that you want to do `add1 + add2` without using `+`, using `++` instead? — crashmstr, Feb 19 '14 at 19:11
@JoshEngelsma I don't think operator overloading has anything to do with this. — crashmstr, Feb 19 '14 at 19:12
See also genial answer here: ["How to add two numbers without using ++ or + or another arithmetic operator"](http://stackoverflow.com/questions/1149929/how-to-add-two-numbers-without-using-or-or-another-arithmetic-operator) — Ivan Aksamentov - Drop, Feb 19 '14 at 19:19
@crashmstr my bad, I misread the question as I was skimming through — Josh Engelsma, Feb 19 '14 at 19:56

score 4 · Answer 1 · answered Feb 19 '14 at 19:12

4

Use a for loop.

e.g.

 for (; add1; add1--, add2++);

add2 will be add1 + add2 assuming add1 is positive

Similar idea for subtraction

answered Feb 19 '14 at 19:12

Ed Heal

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score 2 · Accepted Answer · answered Feb 19 '14 at 19:15

2

It is obvious that you need to use either loops or recursive functions. For example

int add1;
int add2;
cout << "Please enter the 2 numbers you wish to add" << endl;
cin >> add1;
cin >> add2;

int sum = add1; 
for ( int i = 0; i < add2; i++ ) ++sum;

int diff = add1; 
for ( int i = 0; i < add2; i++ ) --diff;

std::cout << "sum is equal to: " << sum << std::endl;  
std::cout << "difference is equal to: " << diff << std::endl;  

return 0;

answered Feb 19 '14 at 19:15

Vlad from Moscow

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Thanks! This makes sense. For loops are still very new too me so I was confused – Moojave Feb 19 '14 at 19:16

Element808 · Answer 3 · 2014-02-19T19:31:47.737

You have to use some sort of built in operators to perform this unless you are required to write a token parser and create your own interpreter and compiler. But I'm guessing since the question is quite basic, it's not asking you to do that.

You can simply do this:

int add1;
int add2;
cout << "Please enter the 2 numbers you wish to add" << endl;
cin >> add1;
cin >> add2;

//perform addition using increment operator
cout << (add1 += add2);

return 0;

EDIT - added decrement operator with less than or equal to 0 if/else:

int add1;
int add2;
int sub1;
int sub2;

cout << "Please enter the 2 numbers you wish to add" << endl;
cin >> add1;
cin >> add2;

//perform addition using increment operator
cout << (add1 += add2);

cout << "Please enter the 2 numbers you wish to subtract" << endl;
cin >> sub1;
cin >> sub2;

if((sub1 - sub2) <= 0)
{
    cout << "Number is less than or equal to 0." << endl;
}
else
    cout << (sub1 -= sub2);


return 0;

Remember, there's no reason to make it overly complicated. If you want to try a for loop to get this done then it's fine but, in my opinion, it's overdoing it for the task. As a programmer, not only is your job to solve problems, but to solve them in the best possible way. — Element808, Feb 19 '14 at 19:37

Addition and subtraction using increment and decrement operators. C++

3 Answers3