Member Avatar for iConqueror

I have been doing some exercises out of the Head First C# book and have just done this exercise where you write a complete sentence using a while loop. The book dosent explain how the while loop puts together the string. I am looking if someone could please explain the logic to me and the process the method uses to create this string. I understand that 'x' has been set to 0 and that the 'while' condition is that while x < 4 run the loop. It confuses me with the logic of this one.

Here is the method:

private void button1_Click(object sender, EventArgs e)
        {
            int x = 0;
            String poem = "";

            while(x < 4)
            {
                poem = poem + "a";//1.

                if(x < 1)//2.
                {
                    poem = poem + " ";
                }

                poem = poem + "n";//3.

                if(x > 1)
                {
                    poem = poem + " oyster";
                    x = x + 2;
                }

                if(x == 1)
                {
                    poem = poem + "noys ";
                }

                if(x < 1)
                {
                    poem = poem + "oise ";
                }
                x = x + 1;
            }
            MessageBox.Show(poem);
        }
    }

Thankyou

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Dani AI

Generated

posted the code and gave a clear iteration-by-iteration readout. The source of the "weird" behavior is not magic: the loop body both appends pieces to the text and sometimes changes the loop counter itself. That combination plus the exact ordering of the append statements produces the surprising sequence of pieces. The walkthrough from shows how the string grows; the important extra points are about how C# handles strings and about safe loop control.

In C# strings are immutable: using poem = poem + "x" creates a new string each time. For a few concatenations that's fine, but repeated appends inside loops allocate many temporaries. A clearer and more efficient pattern is StringBuilder, which accumulates without reallocating on each append. Example pattern:

var sb = new System.Text.StringBuilder();
int x = 0;
while (x < 4)
{
    sb.Append('a');
    if (x < 1) sb.Append(' ');
    sb.Append('n');
    // handle other branches here without surprising side effects
    x++;
}
string poem = sb.ToString();

A second source of confusion is modifying the loop index inside the loop (for example x = x + 2). That is perfectly legal, but it changes the expected sequence of x values and can cause entire branches to never run. For clearer code prefer a single, consistent updater (a for loop or a single x++ at the end) or use an explicit break when you want to exit early. Put the special-case logic in named helper methods or use flags so the control flow is obvious.

Practical troubleshooting tips: step through with the debugger and watch x and the string after each append, or temporarily insert trace prints. For production code, use StringBuilder, avoid changing the loop counter in multiple places, and give variables descriptive names so the flow is easier to follow.

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Member Avatar for hericles

It should be fairly understandable if you buld the string yourself, keeping track of x at the same time but I'll try to give a coherent explanation.

On the first loop x == 0
an A is always added so "a" becomes the first letter.
X < 1 so a space is added : "a "
An 'n' is always added: "a n"
Only the x < 1 if statement is called as x == 0 so oise is added: 'a noise '

Second loop, x = 1
an 'a' is always added: 'a noise a'
an 'n' is always added: 'a noise an'
the only if statement to fire is x == 1 so noys is added: 'a noise annoys '

Third loop x == 2
add an a
add an n : 'a noise annoys an'
x > 1 if statement adds 'oyster' : 'a noise annoys an oyster'
x increments to 4 so loop exits

Does that help?

Member Avatar for iConqueror

That helps! thankyou!

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