Thread: rand() error??

hello all, I have this function which is posted below, and the second time the while loop goes through it crashes. On MSVC++ it terminates the dos window, and on unix I get a floating exeption error.

I've pin pointed the problem to be where I get the second random number...near the buttom of the function...any ideas??

axon

Code:

void readInFileAndGetChars(string fileName, char text[], int& sum)
{
	//declaring variables
	int i;

	ifstream inStream;

	inStream.open(fileName.c_str()); //open user chosen file

	if ( inStream.fail() ) { //check if file opened right
		cout << "Input file opening for " << fileName << " failed.  Exiting...\n\n";
		exit(-1);
	}

	for ( i=0; i<MAX_SIZE; i++ ){ //input file into the array
		inStream.get(text[i]);
	}
	
	cout << endl << endl << fileName << " consists of " << MAX_SIZE << " characters.\n\n "
	     << endl;
}

//=============================================
void generateOutput(char text[], int window, int length, int sum)
{
	//declaring arrays
	char *windowArr = new char[window]; //window array
	int allChars[127];

	//declaring variables
	int randomPosition = (rand()/2);//( rand()%MAX_SIZE ); //get random number
	bool notDone = true;
	int i, j, temp;
	int count2 = 0; //couter for how many times through loop
	
	while(notDone)
	{
		int randChar=0;
		int count = 0;	//counter for comparison part
		
		int sum2 = 0;	//sum for all characters that follow window
		char printChar; //randomly chosen charcter that will follow window

		
		for( i=0; i<window; i++){ //match random position characters with window
			if(count2 == 0){	
				windowArr[i] = text[randomPosition + i];
			}else{
				
				windowArr[i] = windowArr[i+1];
				windowArr[window-1] = printChar;
				
			}
		}

		for( i=0; i<127; i++){ //set every element to 0
			allChars[i] = 0;
		}
		
		for( i=0; i<MAX_SIZE; i++){ //COMPARISON
			count = 1;
			if( windowArr[0] == text[i] ){
				for( j=1; j<window; j++ ){
					if( windowArr[j] == text[i+j] ){
						count++;
					}else{ break;}
					if( count == window ){
						allChars[ text[j+i+1]]++; //to get next char and add 1 to it
						break;
					}else{continue;}
				}
			}
		}
		
		for(i=0; i<127; i++){  //get sum of characters which appear at least 1 time
			if(allChars[i] > 0){
				sum2 += allChars[i];
			}
		}
		
		char *lastChar = new char[sum2]; //declare array to hold characters that appear after window
		temp = sum2;
		
		for( i=0; i<127; i++){ //put all characters that appear at least once
			if( allChars[i] > 0 ){ //into an array
				while( temp != -1 ){
					for( j=1; j<=allChars[i]; j++){
						lastChar[i-i+temp-j] = (char)i;
					}
					temp = temp - (1*allChars[i]);
					break;
				}			
			}
		}
		/****The PROBLEM IS IN THE LINE BELOW***/
		randChar = (rand()%sum2); //get random position for next char
		printChar = lastChar[randChar];
		
		cout.flush() << printChar;

		count2++;
		
		if( count2 == length ){
			notDone = false;
		}
	}
}

should I delete the dynamic arrays declared in the while loop at its end?

if not, how do I solve the problem?

axon

Oh I see what you're syaing now...yes windowArr[i+1] does go over but I don't see how text[ randomPosition + 1] does...text is an array of 500000 elements...anyhow, will this work to fix the windowArr problem?

Code:

for( i=0; i<window; i++){ //match random position characters with window
			if(count2 == 0){	
				windowArr[i] = text[randomPosition + i];
			}else{
				if( i != (window-1)){ 
					windowArr[i] = windowArr[i+1];
				}
				windowArr[window-1] = printChar;
				
			}
		}

that is what I put in, but I still get the mistake,

axon

that was specified by my assignment! :-(

axon

first of all...the assignment...in short form is as follows...user pics a file to analize(files provided) than enters a window size, and output length.

Now, the program opens the specified file, puts the first 500000 characters of that file into an array, randomly picks a position in that array and takes a window size number of characters from it.

For example...if the array contained {this is the thou those that!} and the window size was 2, and the random position would be 0, the program would put the first "th" into another array.

Next part is to step through the array containing the 500000 characters to look for any occurences of "th" and taking the character that follows it. Then these characters are sumed up, and put into another array...one of these characters is then randomly hose and printed out...the windo is then moved one to the right, and the whole process repeated again, until the output length of characters is reached.

THATS just the first part...I hope you understand...by the way I think this is a VERY tough assignment for a first c++ class! anyhow, if you are still unclear here is a link to the assignment.

in the zipped file I included input.txt because that is what I use for debugging...

thanks for the help

axon

sh&t! sum2 is equal to zero! I don't know how come...!?!? first time through the loop it is fine. And I'm not getting divide by 0 problem...the program just terminates


grumble grumble grumble

axon <--- tired and ........ed off - yet optimistic

OK I see what is going on...its not finding another instance so it sets sum2 = 0... to partially fix that I replaced that first loop with

Code:

if(count2 == 0){
      for( i=0; i<window; i++){ //match random position characters with window
      windowArr[i] = text[randomPosition + i];
      cout << windowArr[i];
      }
}else{
	for( i=0; i<(window-1); i++){ //match random position characters with window
	windowArr[i] = windowArr[i+1];
	windowArr[printChar];
	}
}

and if you put window size=2 and 20 output length it works well, but not to the desired effect....any help with the program it self?

thanks a bunch for your help codeplug!

axon