encryption algorithm

This is a discussion on encryption algorithm within the C Programming forums, part of the General Programming Boards category; I am fairly new to coding in c. I am having trouble writing a function to read a character and ...

  1. #1
    Registered User
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    Dec 2006
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    Question encryption algorithm

    I am fairly new to coding in c. I am having trouble writing a function to read a character and encrypt the character so that
    A becomes Z
    B becomes Y
    C becomes X
    and so on.....
    same with lowercase letters

    Heres what i thought would work but i guess not. It only for capitals. I tried using ascii code but im pretty sure there is a simpler way to code this encryption process. thanks a lot.

    Code:
    char encryptAlpha (char strChar)
    {
    
    //	Local Definitions
    	int i;
    	int j; 
    
    //	Statements
    	if ((strChar > 64) && (strChar < 91))
    	{
    		for (i = 65, j = 90; i < 91, j > 64; i++, j--)
    		{
    			if (strChar == i)
    				strChar = j;
    		}
    	}
    return strChar;
    }// encryptAlpha

  2. #2
    int x = *((int *) NULL); Cactus_Hugger's Avatar
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    Jul 2003
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    Banks of the River Styx
    Posts
    902
    I'll need to look at it a bit more, but:
    Don't use actual numeric values for letters in your code. It makes the whole thing unintelligable. Don't write:
    Code:
    char x = 97;
    Write:
    Code:
    char x = 'a';
    It'll also make your code that much more portable should you happen across a weird platform where 'a' != 97.

    _If_ I'm reading the code right, it looks like a simple substitution cipher where:
    a = z
    b = y
    c = x
    etc. ?
    If so, don't use a for() look in the inside, it can be done with some if()s and a subtraction statement. (The function should be constant time)
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
    The best way to accelerate an IBM is at 9.8 m/s/s.
    recursion (re - cur' - zhun) n. 1. (see recursion)

  3. #3
    aoeuhtns
    Join Date
    Jul 2005
    Posts
    581
    Your expression, i < 91, j > 64 is equivalent to j > 64, because the comma operator returns only the value of the second expression. You'd probably be better off replacing the for loop with strChar = 'Z' - (strChar - 'A'); anyway, since that's a simpler way of achieving the same goal. Realize that the expression 'Z' is just just a cute way of writing the number 90, assuming you're using the ASCII character set. In fact, it'd be more readable to rewrite your 9th line with if ((strChar >= 'A') && (strChar <= 'Z')).
    There are 10 types of people in this world, those who cringed when reading the beginning of this sentence and those who salivated to how superior they are for understanding something as simple as binary.

  4. #4
    Registered User
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    Dec 2006
    Posts
    11
    Got it figured out!! thanks for your guys input. Here is the code i finished with, Just another question. If you think it should receive any changes or could improve please say so. I am always up to helpful criticism and am always looking to improve my coding. thanks again.

    Code:
    char encryptAlpha (char strChar)
    {
    
    //	Local Definitions
    	char firstChar;
    	char lastChar;
    
    //	Statements
    	if ((strChar >= 'A') && (strChar <= 'Z'))
    	{
    		firstChar = 'A';
    		lastChar  = 'Z';
    		{
    			while ((firstChar <= 'M') && (lastChar >= 'N'))
    			{
    			if (strChar == firstChar)
    				strChar = lastChar;
    			else if (strChar == lastChar)
    				strChar = firstChar;
    
    			firstChar++;
    			lastChar--;
    			}
    		}
    	}
    
    	if ((strChar >= 'a') && (strChar <= 'z'))
    	{
    		firstChar = 'a';
    		lastChar  = 'z';
    		{
    			while ((firstChar <= 'm') && (lastChar >= 'n'))
    			{
    			if (strChar == firstChar)
    				strChar = lastChar;
    			else if (strChar == lastChar)
    				strChar = firstChar;
    
    			firstChar++;
    			lastChar--;
    			}
    		}
    	}
    return strChar;
    }// encryptAlpha

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