Postfix_prefix

15y2kVisual Basic .NET

In the following program I entered 10, results are 10, 11, 12 and 11 respectively. Please explain the reason.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace prefix_postfix1
{
class Program
{
static void Main(string[] args)
{
string entry;
int w, x, y, z, n;

Console.Write("Enter an integer ");

entry = Console.ReadLine();
n = Convert.ToInt32(entry);

w = n;
n++;
Console.WriteLine("{0}", w);//output=10

x = n;
++n;
Console.WriteLine("{0}", x);//output=11

y = n;
n--;
Console.WriteLine("{0}", y //output=12

z = n;
--n;
Console.WriteLine("{0}", z);//output=11

Console.ReadKey();
}
}
}

9 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes15y ago
I was using 'current' operation in the sense of the main operation on 'n'. Incrementing or decrementing is, of course, also an operation on 'n' but is sometimes only a subsidiary operation.

So, if you have this line:

Console.WriteLine(n++);

or this line:

Console.WriteLine(++n);

then the main operation on 'n' is writing it to the console and incrementing it is a subsidiary operation.

It matters here whether postfix or prefix incrementation is used, because it will affect the value which gets printed.

However, if you have this line:

n++;

or, this line:

++n;

then the current operation on 'n' is simply incrementing it.

It makes no difference in this case whether postfix or prefix incrementation is used, because it's independent of (i.e. doesn't affect) any other operation.
15y ago
What is meant by "current operation on 'n'" because increments or decrements also an operation. In my view there is only one operation in a statement that is increments or decrements.
Vulpes15y ago
If you're using postfix or prefix notation in your code then, in order to predict the output, you have to understand how they work.

Prefix notation (++n, --n) increments or decrements 'n' before carrying out the current operation on 'n'.

Postfix notation (n++, n--) increments or decrements 'n' after carrying out the current operation on 'n'.
15y ago
Hi Vulpes is there any way to predict the output rather than interpreting it. Because when location of the variable changes output changes. You can see the 1st program in this thread.
Vulpes15y ago
n starts off at 10 and so this line prints 10 and then increments n to 11:

Console.WriteLine("A = {0}", n++);//A=10

n is 11 but is then incremented to 12 by this line before it is printed:

Console.WriteLine("B = {0}", ++n);//B=12

n is 12 and so this line prints 12 and then decrements n to 11:

Console.WriteLine("C = {0}", n--);//C=12

n is 11 but is then decremented to 10 by this line before it is printed:

Console.WriteLine("D = {0}", --n);//D=10
15y ago
Hi Narayan how to interpret this result. I entered 10, results are A=10, B=12, C=12 and D=10.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
string entry;
int n;

Console.Write("Enter an integer ");

entry = Console.ReadLine();
n = Convert.ToInt32(entry);

Console.WriteLine("A = {0}", n++);//A=10

Console.WriteLine("B = {0}", ++n);//B=12

Console.WriteLine("C = {0}", n--);//C=12

Console.WriteLine("D = {0}", --n);//D=10

Console.ReadKey();
}
}
}

The output must be according to my understanding A=10, B=11, C=11 and D=10
Narayan15y ago
Yes you are right as they have written in different statement.

If you would have written something
w=n++;
or
x=++n;
result will be different.
15y ago
Hi Narayan thank you for your replay. Please see whether my understanding is correct.

That mean 2nd statement is just copying the calculated value of 1st statement.

3rd statement is just copying the calculated value of 2nd statement.

4th statement is just copying the calculated value of 3rd statement.
Narayan15y ago
first n=10
you have assigned it to w, so value of w=10.
Then n++; will change the value of n to 11 and you have assigned it to x
So value of x will be 11.

Then ++n again value of n is changed to 12 and you have assigned it to y so value will be 12

then n-- will change the value of n to 11 and has been assigned to z , so value of z will be 11