Encryption problem

[drater]

I am encrypting text from a file and storing the newly encrypted message in a text file.

If the ith char is an uppercase letter, shift it to be the char x[i] away where x = {3, -1, 0, 2, -2}
If ith char is a lower case letter, shift it to be the char y[i] away where y = {2, 4, -1, -2}
If ith char is a digit, shift it to be the char z[i] away where z = {1, -1, 2}
If a char is a non-letter and non-digit, then it does not change

Also A + 1 would become Z, z - 1 becomes a, and 9 + 1 becomes 0

Example:
“Hello!” would have the “H” shift 3 further away (“H” becomes “K”), “e” would be shift 4 away (becoming “i”), “l” shifts -1 away (becoming “k”), the second “l” shifts -2 away (“l” becomes “j”), “o” shifts 2 away since we reached the end of the y array (“o” becomes “q”). and “!” remains the same.

So far I have:

#include <stdio.h>

int main()
{

	/*	array for shifting an uppercase letter */
	int x[] = {3, -1, 0, 2, -2};

	/*	tarray for shifting a lowercase letter */
	int y[] = {2, 4, -1, -2};

	/*	array for shifting a digit */
	int z[] = {1, -1, 2};

	int *xNext = x; 
	int *yNext = y; 
	int *zNext = z;

	FILE *fp1, *fp2;			// file pointers

	const int xArraySize = 5;
	const int yArraySize = 4;
	const int zArraySize = 3;

	int totalChars = 0;
	int iter = 0;

	char inputTextArray[5000];
	char inputFilename[30];		// Character Array to hold the users specified input file name
	char currentCharacter;		//current character input from the file
	char outputFilename[30];	// holds the users specified output file name
	char *textArrayPointer = inputTextArray;

	printf("Enter the name of the file to be scanned: "); 	
	scanf("%s", inputFilename);			// Scans the input file specified by the user 		
	fp1 = fopen(inputFilename, "r");	// open the file as read-only 

	
	printf("Enter the name of the file you wish to copy %s to: ",  inputFilename);	// ask user for outputFilename (copy of inputFilename)
	scanf("%s", outputFilename);
	fp2 = fopen(outputFilename, "w");	// open output file, write-only
	

	while((currentCharacter = getc(fp1)) != EOF)
	{
		*textArrayPointer = currentCharacter;
		textArrayPointer++;
	} 
	


	 while(*textArrayPointer != '\0')
	{
		/*	Check for capital letters A through Z
			A in ASCII is 65, and Z is 90	*/
		if (( *textArrayPointer >= 65 ) && ( *textArrayPointer <= 90 ))
		{

			iter = totalChars % xArraySize;
			while(iter-- != 0)
			{
				xNext++;
			}

			*textArrayPointer = *textArrayPointer + *xNext;
			if ( *textArrayPointer < 65)
			{
				*textArrayPointer += 26;
				
			}
		
			if ( *textArrayPointer > 90)
			{
				*textArrayPointer -= 26;
			}


			putc(*inputTextArray, fp2);
		}

		/*	Check for lower case letters a through z
			a in ASCII is 97, and z is 122	*/
		else if (( *textArrayPointer >= 97 ) && ( *textArrayPointer <= 122 ))
		{

			iter = totalChars % yArraySize;
			while(iter-- != 0)
			yNext++;
		
			*textArrayPointer = *textArrayPointer + *yNext;
			if ( *textArrayPointer < 97)
			{
				*textArrayPointer += 26;
			}

			if ( *textArrayPointer > 122)
			{
				*textArrayPointer -= 26;
			}

			putc(*inputTextArray, fp2);
		}

		/*	Check for numbers 0 through 9
			0 in ASCII is 48, and 9 is 57	*/
		else if (( *textArrayPointer >= 48 ) && ( *textArrayPointer <= 57 ))
		{

			iter = totalChars % zArraySize;
			while(iter-- != 0)
			zNext++;

			*textArrayPointer = *textArrayPointer + *zNext;
			if ( *textArrayPointer < 48)
			{
				*textArrayPointer += 26;
			}

			if ( *textArrayPointer > 57)
			{
				*textArrayPointer -= 26;
			}

			putc(*inputTextArray, fp2);
		}

		/*	The criteria did not meet the previous
			conditions. The character must be a symbol	*/
		else 
		{
			putc(*inputTextArray, fp2);
		}

		*textArrayPointer++;
		totalChars++;


	}
}

I get a run time error and I am not sure what I have done wrong. Any assistance would be much appreciated.

[tabstop]

while((currentCharacter = getc(fp1)) != EOF)
	{
		*textArrayPointer = currentCharacter;
		textArrayPointer++;
	} 
	


	 while(*textArrayPointer != '\0')

You need to "rewind" your pointer before starting this loop in red here. (Also, checking that you don't run off the end of your buffer would be a good idea.)

[drater]

I added:

	while((getc(fp1)) != EOF)
	{
		textArrayPointer--;
	}

after:

while((currentCharacter = getc(fp1)) != EOF)
	{
		*textArrayPointer = currentCharacter;
		textArrayPointer++;
	}

but I don't think that was the correct solution because my output file has 4,896 "T"'s when the input file had only 85 characters.

[arpsmack]

Why are you reading the characters into an array? You're processing them one at a time anyway...