Why is the variable value changing automatically?

Question

This is my code

    int front=-1, rear=-1, CQUEUE[MAX];
    int isFull()
    {
      if((rear=MAX-1 && front==0) || front==rear+1)
        return 1;
      else
        return 0;
    }
    void enQueue()
    {
      printf("\nValue of rear=%d front=%d",rear,front);
      char ch;
      if(!isFull())
      {
        printf("\nValue of rear=%d front=%d",rear,front);
      ......

This is the output on calling the function enQueue()

Value of rear=-1 front=-1
Value of rear=0 front=-1

The value of rear is getting increased by 1 although I'm not increasing it manually.

That almost always points to an instance where you are writing beyond the end of some array you have declared, or otherwise write more to a stack variable than it will hold causing the additional bytes to overwrite your other variable storage space giving the illusion that something magically changed -- it didn't, you just invoked *Undefined Behavior* and are seeing the result... (or in this case you mess up an `=` that should be an `==`). Enabling compiler warnings would have pointed that out for you. — David C. Rankin, Sep 28 '20 at 04:56

score 1 · Accepted Answer · answered Sep 28 '20 at 04:56

1

Look at your first if statement.

if (rear=MAX-1  ...)
// maybe better if you type:
if (rear==MAX-1 ...)

answered Sep 28 '20 at 04:56

dunajski

381
3
15

score 1 · Answer 2 · answered Sep 28 '20 at 04:57

1

You are using the assignment operator = where you should be using the eq comparison operator == in isFull

int isFull()
{
  if((rear==MAX-1 && front==0) || front==rear+1)
    return 1;
  else
    return 0;
}

answered Sep 28 '20 at 04:57

Sevan Golnazarian

827
9
18

Why is the variable value changing automatically?

2 Answers2