Chapter 5 Exercises

Chris Beach · August 18th, 2003, 08:20 AM

1) b & d can be implicitly converted, a can't short isn't large enough, c not sure.
2) if there are less than 256 colours, then you could base the enum on byte
3)

Code:

    struct imagNum
    {
        public double real,imag;
    }
    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    class Class1
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            imagNum coord, temp;
            double realTemp2, arg;
            double realMin=-0.6,realMax=1.77,imagMin=-1.2,imagMax=1.2;        //limits
            double realInc=0.03,imagInc=0.05;
            //work out inc's
            imagInc=(imagMax-imagMin)/48;
            realInc=(realMax-realMin)/78;  //uh why not 79??

            int iterations;
            for (coord.imag=imagMax;coord.imag>=imagMin;coord.imag-=imagInc)
            {
                for (coord.real=realMin; coord.real<=realMax;coord.real+=realInc)
                {
                    iterations=0;
                    temp=coord;
                    arg=(coord.real*coord.real)+(coord.imag*coord.imag);
                    while((arg<4)&&(iterations<40))
                    {
                        realTemp2=(temp.real*temp.real)-(temp.imag*temp.imag)-coord.real;
                        temp.imag=(2*temp.real*temp.imag)-coord.imag ;
                        temp.real=realTemp2;
                        arg=(temp.real*temp.real)+(temp.imag*temp.imag);
                        iterations+=1;
                    }
...

though I can't see why you'd do it this way, only one bit of code as gotten simpler!
4) No quotes around the string.

Chris Beach · August 18th, 2003, 09:04 AM

5)

Code:

            string inString, outString="";
            Console.WriteLine("Please enter a string:");
            inString=Console.ReadLine();
            char[] inChars=inString.ToCharArray();
            int i=inChars.Length-1;
            while (i>=0)
            {
                outString=outString + inChars[i];
                i--;
            }
            Console.WriteLine("'{0}' reversed is '{1}'",inString,outString);

I tried for ages to do it as a for loop but couldn't
Whats wrong with:

Code:

for(int i=inChars.Length-1;i=0;i--)

Chris Beach · August 18th, 2003, 09:12 AM

6)

Code:

string inString,outString;
Console.WriteLine("Please enter a string:");
inString=Console.ReadLine().ToLower();
outString=inString.Replace("no","yes");
Console.WriteLine(outString);

Don't like it though, can I make the replace bit case insensitve?

Chris Beach · August 18th, 2003, 09:23 AM

7)

Code:

string inString, outString="";
Console.WriteLine("Please enter a string:");
inString=Console.ReadLine();
string[] words;
char[] sep={' '};
words=inString.Split(sep);
foreach (string word in words)
{
  outString=outString + "\"" + word + "\"";
}
Console.WriteLine("New String: {0}",outString);

Ok that works but a few q's
1) why do I have to put outString="" in the decleration? in bombs if i don't...
2) do I have to do the Split exactly like that? I tried just .Split(' ') but it didn't like that...seems long winded.

sweetj · August 20th, 2003, 11:25 PM

1)on C bool and string can never be implicitly converted
5)

         string inString, outString="";
            int i;
            Console.WriteLine("Please enter a string:");
            inString = Console.ReadLine();
            char[] inChars = inString.ToCharArray();
            for (i = inChars.Length - 1; i >= 0; i--)
            {
                outString=outString + inChars[i];
            }
            Console.WriteLine("'{0}' reversed is '{1}'", inString, outString);

That is if you wanted to do it in a for loop, I believe that works.

7)

         string inString, outString="";
            Console.WriteLine("Please enter a string:");
            inString = Console.ReadLine();
            string[] words;
            words = inString.Split();
            foreach (string word in words)
            {
                outString = outString + "\"" + word + "\" ";
            }
            Console.WriteLine("Everything with quotes: {0}", outString);

I think this works too, and slightly shorter.

Everything else looks great. Thanks for posting this. Because for some reason when I tried to do these questions the day after I read it, I was drawing a blank. Your answer 5 really helped jog my memory ;)

From what my friends tell me the reason you need outString="". Is that c# likes it if you can define your variables, so that you can manipulate it even if it is a blank space. Before in languages like VB you didn't have to, and it cause alot of crashing problems. Btw this is what someone told me off hand so it might not be 100% right.

Chris Beach · August 21st, 2003, 03:33 AM

I knew I should be able to do it in a for loop! thx!

Yea after posting and reading more I found the reason for the need of outString="".

The string outString, actually does pretty much naff all! and more importantly it doesn't allocate any memory for outString, so by putting "" into outString all the memory allocation stuff is done. Which half explains it, but why does this have to be done before the loop, why can't it be done on the first loop? maybe sommit to do with the compiler optimzations...

melakka · October 17th, 2003, 11:16 AM

5) neatest solution is:

Console.Write("Please enter string : ");
string userstring=Console.ReadLine();
Console.Write("String backwards is : ");
for (int i=userstring.Length;i>0;i--) //loop back through string
{Console.Write(userstring[i-1]);} //and write each letter

Chris Beach · October 17th, 2003, 11:22 AM

mmm maybe, but you haven't actually reversed the string, so depending on your interpretation of the question its either right or wrong:)

melakka · October 22nd, 2003, 07:54 AM

5)
I agree the wording implied writing a full string rather than characters, so here is amended version:

Console.Write("Please enter string : ");
string userstring=Console.ReadLine();
string backwards="";
for (int i=userstring.Length;i>0;i--)
{backwards+=userstring[i-1];}
Console.Writeline("String backwards is : " + backwards);