Why wont this square root properly?

[j1997]

a=((s1.rel)*(s2.rel))-((s1.img)*(s2.img));
b=((s1.rel)*(s2.img))+((s2.rel)*(s1.img));
c=((sqrt(a * a) + (b * b)));
d=((atan (b/a)*((57.2958))));
cout<<"nMultiplication: "<<"("<<c<<")"<<"+"<<"("<<d<<")"<<"i";

[keskiverto]

Define "properly".

You have quite a lot of parentheses. Are they all necessary?

Your equation for 'c' is equivalent to c = abs(a) + b*b;. Is that intentional?

[j1997]

i need c to equal the square root of a squared + b squared but when i run the program it gives me the wrong value?
In terms of the parentheses the are all necessary.

[Peter87]

Not sure what it is that you're trying to compute but it looks similar do a distance calculation.

   |\
 a | \ c
   |  \
   |___\
     b
     _______
c = √a² + b²

If that's the case you need to move the addition of b*b inside the parentheses of the square root call. I honsestly think you're using way too many parentheses here. You're probably confusing yourself.

// Is this what you want?
c = sqrt(a * a + b * b);

[Chervil]

I'd definitely get rid of the excess parentheses - they serve to obscure what is going on - thus increasing the likelihood of accidental mistakes.

Order of precedence of the various operators takes care of the order in which things are done here.

a = s1.rel*s2.rel - s1.img*s2.img;
b = s1.rel*s2.img + s2.rel*s1.img;

c = sqrt(a*a + b*b);
d = atan(b/a) * 57.2958;

See Precedence of operators
http://www.cplusplus.com/doc/tutorial/operators/

[j1997]

thank you all for your help, solved now! and ive removed the parentheses hahaa

[lastchance]

If you are going to do it this way you should use atan2(y,x) rather than atan(x): you will get an answer in the correct quadrant (otherwise you will be wrong 50% of the time) and you won't crash when a = 0.

Given what you are doing you would be better with complex numbers: see the advice given to you in your other post.

What you have written in your answer line is also patently wrong: that is not a polar form. You want something like, e.g.,
cout << "Multiplication: " << c << " exp( " << d << " i)" << endl;
or, if you must,
cout << "Multiplication: (modulus, argument) = (" << c << ", " << d << " )" << endl;

For complex numbers in polar form leave the angle in radians - there is no need for the extra multiplying factor of 57.2958, which would be incorrect once it is inside the complex exp().