Programming to Program

To learn to program you must program. This is a concept that a lot of time flies over beginners. They get excited about coding, but instead of grinding out some code, they read tutorial after tutorial, or search through the web looking for something that isn't there.

But, once you realize this concept, what do you do about it? It can be pretty tough to think up a program to write yourself. One of the things that I have learned is that often, if you aren't in a class or some environment that forces you to learn, i.e. gives you tasks or assignments, it can be difficult to push yourself.

Probably the best learning tool that can be found on the internet is programming challenges. These appear in books and forums. Someone gives a list of programming quandaries as a challenge to other programmers to solve. These can greatly help you learn to program faster, sharper, and more efficiently.

A great place to find these are forum threads. Right now Programming Forums has some great challenges out there. There is also an e-book that has challenges in it, with robotic judges as well.
These challenges are your best friend, they invite you to program, and even give you what to program. You can't help but learn. Great Stuff!! If you have any sites that you have found, or have made yourself, post them below!

what reversing strings can teach us...

Reversing a string is almost a standard interview question for internships and other jobs requiring programming. What is interesting is that there are many ways to reverse a string, which we will look at below. The answer to which method is the best reveals an interesting lesson in computer science.

Alrighty, so you have your scripting languages that make it mind numbingly easy to reverse a string, in Python the answer is simply mystring[::-1] and voila, string reversed. Probably the most standard way in C++ is to simply make a temp array and iterate through your string, putting each letter from the back to the front in your temp array. This is a satisfactory answer, but it won't win you any brownie points either. The shortest code in C would have to use recursion.

# include

void recurs_string(char * );

/* Definition of the recurs_string() function */

void recurs_string(char *string)
{
if (*string)
{
recurs_string(string+1);
putchar(*string);
}
}

void main(void)
{
char str[100];
printf("\n Input a string: ");
gets(str);
printf("\n Reverse of the string: %s", str);
printf("\n Reverse string is: ");
recurs_string(str);
}

(I got this from here, because I am too lazy to write my own)

While recursion may look impressive, it uses a lot of stack, so it really isn't the best way either. The best way to reverse a string is below.

public string Reverse(string str)
{
// convert the string to char array
char[] charArray = str.ToCharArray();
int len = str.Length - 1;
for (int i = 0; i < len; i++, len--)    {             
  charArray[i] ^= charArray[len];                
  charArray[len] ^= charArray[i];                
  charArray[i] ^= charArray[len];    
}         
return new string(charArray); }         

Now if you are me when you saw this code you were like "what the heck is '^=' ?" that happens to be the XOR (exclusive OR) operator. XOR is a logic operator that returns a one if only one of the two input s is a one. for example 1 XOR 0 = 1, 0 XOR 1 = 1, but 1 XOR 1 = 0. Why this is useful is that XORing two elements three times performs a bitwise switch of those two elements, lets take a look.



1100101
XOR 0111010

= 1011111
XOR 0111010

= 1100101

So you can see, performing XOR operations on two individual characters actually switches there values. This has a practical learning application. Sometimes, the best implementation of a solution can be achieved using low-level logic operations, such as arithmetic shifts, bitwise logic operatiors such as AND, OR, XOR, etc. and binary addition and subtraction. keep this in mind the next time you are trying to optimize your code (and make yourself king of the geeks by writing something that is faster than everybody elses code, and only you can understand.)