|
|
|
|
|
|
|
when an odd number is read. The counter in this example is an event counter; it is initialized to 0 and incremented only when a certain event occurs. The counter in the previous example was an iteration counter; it was initialized to 1 and incremented during each iteration of the loop. |
|
|
|
 |
|
|
|
|
Event Counter A variable that is incremented each time a particular event occurs. |
|
|
|
|
|
|
|
|
Keeping Track of a Previous Value |
|
|
|
|
|
|
|
|
Sometimes we want to remember the previous value of a variable. Suppose we want to write a program that counts the number of not-equal operators (!=) in a file that contains a C++ program. We can do so by simply counting the number of times an exclamation mark (!) followed by an equal sign (=) appears in the input. One way in which to do this is to read the input file one character at a time, keeping track of the two most recent characters, the current value and the previous value. In each iteration of the loop, a new current value is read and the old current value becomes the previous value. When EOF is reached, the loop is finished. Here's a program that counts not-equal operators this way: |
|
|
|
|
|
|
|
|
//******************************************************************
// NotEqualCount program
// This program counts the occurrences of != in a data file
//******************************************************************
#include <iostream.h>
#include <fstream.h> // For file I/O
int main()
{
int count; // Number of != operators
char prevChar; // Last character read
char currChar; // Character read in this loop iteration
ifstream inFile; // Data file
inFile.open(myfile.dat); // Attempt to open input file
if ( !inFile ) // Was it opened?
{
cout << ** Can't open input file ** // No--print message
< endl;
return 1; // Terminate program
}
count = 0; // Initialize counter
inFile.get(prevChar); // Initialize previous value
inFile.get(currChar); // Initialize current value
while (inFile) // While previous input succeeded...
{ |
|
|
|
|
|