C# 0 The Complete Reference

tos

 to zero. Thus, a zero value in 

tos

 indicates that the stack is empty.

The public 

Push( )

 method puts an element onto the stack. It is shown here:

// Push characters onto the stack.

public void Push(char ch) {

  if(tos==stck.Length) {

    Console.WriteLine(" -- Stack is full.");

    return;

  }

  stck[tos] = ch;

  tos++;

}

The element to be pushed onto the stack is passed in 

ch

. Before the element is added to 

the stack, a check is made to ensure that there is still room in the underlying array. This is 

done by making sure that 

tos

 does not exceed the length of 

stck

. If there is still room, the 

element is stored in 

stck

 at the index specified by 

tos

, and then 

tos

 is incremented. Thus, 

tos

 always contains the index of the next free element in 

stck

.

To remove an element from the stack, call the public method 

Pop( )

. It is shown here:

// Pop a character from the stack.

public char Pop() {

  if(tos==0) {

    Console.WriteLine(" -- Stack is empty.");

    return (char) 0;

  }

  tos--;

  return stck[tos];

}

Here, the value of 

tos

 is checked. If it is zero, the stack is empty. Otherwise, 

tos

 is 

decremented, and the element at that index is returned.

Although

Push( )

 and 

Pop( )

 are the only methods needed to implement a stack, some 

others are quite useful, and the 

Stack

 class defines four more. These are 

IsFull( )

,

IsEmpty( )

,

Capacity( )

, and 

GetNum( )

, and they provide information about the state of the stack. They 

are shown here:

// Return true if the stack is full.

public bool IsFull() {

  return tos==stck.Length;

}

// Return true if the stack is empty.

public bool IsEmpty() {

  return tos==0;

}

// Return total capacity of the stack.

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