How to swap two variable values?

Question

I'm writing a complex program that calculates change in potential energy( ΔPE= mgΔh ).

Console.WriteLine("Mass in kg");
string cmMa = Console.ReadLine();
double cMass;
if(!Double.TryParse(cmMa, out cMass) )
{
    Console.WriteLine("Only numbers!");
    Console.ReadLine();
}
Console.WriteLine("First height in m");
string cfH = Console.ReadLine();
double fH;
if(!Double.TryParse(cfH, out fH))
{
    Console.WriteLine("Only numbers!");
    Console.ReadLine();
}
Console.WriteLine("Second height in m");
string csH = Console.ReadLine();
double sH;
if(!Double.TryParse(csH, out sH))
{
    Console.WriteLine("Only numbers!");
    Console.ReadLine();
}
double ch = fH - sH;
Console.WriteLine("Intermediate result: Change in height(Δh)= "+ch+" m" );
Console.ReadLine();
double ng = 9.81;  //   m/s^2
Console.WriteLine("CHANGE IN POTENTIAL ENERGY: "+ch*cMass*ng+" J");

At the end, I want to add an if statement that if sH>fH, then their values are swapped. What concept should I apply?

possible duplicate of [Swap two variables without using a temp variable](http://stackoverflow.com/questions/804706/swap-two-variables-without-using-a-temp-variable) — Shishir Gupta, Jul 29 '14 at 11:09

score 3 · Answer 1 · answered Dec 12 '17 at 03:58

To swap values of sH and sF:

sH = Interlocked.Exchange(ref sF, sH);

Class Interlocked is declared in System.Threading namespace.

It allows to swap variables in one line. The swap is atomic, thread-safe.

In terms of performance it is a little bit "slower" than swap using temp variable. It is still lighting-fast. One should not worry unless doing extreme optimization at nano-scale level.

score 1 · Answer 2 · answered Jun 30 '13 at 14:59

1

Store one of the variables in a temp an variable and then swap them:

if (sH > fH) {
   var temp = sH;
   sh = fH;
   fH = temp; 
}

answered Jun 30 '13 at 14:59

Darren

68,902
24
138
144

score 1 · Accepted Answer · answered Jun 30 '13 at 15:03

if (sH > fH) {
  double temp = sH;
  sH = fH;
  fH = temp;
}

The swapping can be accomplished by using a temporary third variable. Store sH in a temporary variable and assign sH to fH. This way the value of sH is cached and not lost when reassigning. Lastly, assign fH to temp. The values are now swapped.

Hope this helps

score 1 · Answer 4 · answered Jun 30 '13 at 15:06

1

Assuming your reason for doing this is so that ch isn’t negative here:

double ch = fH - sH;

Just get the absolute value:

double ch = Math.Abs(fH - sH);

answered Jun 30 '13 at 15:06

Ry-

218,210
55
464
476

score 1 · Answer 5 · edited Sep 16 '16 at 02:42

1

Use:

static void Main(string[] args)
{
    Console.WriteLine("please imput number 1 ");
    int a = Convert.ToInt32(Console.ReadLine());
    Console.WriteLine("please imput number 2 ");
    int b = Convert.ToInt32(Console.ReadLine());

    if (a > b)
    {
        int temp1 = a;
        int temp2 = b;
        b = temp1;
        a = temp2;
    }
}

edited Sep 16 '16 at 02:42

Peter Mortensen

30,738
21
105
131

answered Apr 28 '15 at 20:31

louis

11
1

score 0 · Answer 6 · answered Jun 30 '13 at 15:01

0

Er... Copy A into a tmp variable, copy B into A, copy tmp into B? Since you are dealing with strong parsing, I can't see that anything crazy like an xor-swap (via unsafe integer treatment) would be warranted.

answered Jun 30 '13 at 15:01

Marc Gravell

1,026,079
266
2,566
2,900

score -2 · Answer 7 · edited Sep 16 '16 at 02:41

-2

Try this, but this is not as fast as using a temporary variable:

if (sH > fH)
{
    sH -= fH;
    fH += sH;
    sH = fH - sH;
}

edited Sep 16 '16 at 02:41

Peter Mortensen

30,738
21
105
131

answered Dec 01 '13 at 15:04

Mahesh Rao

1

How to swap two variable values?

7 Answers7