My switch statement doesn't work properly

Question

I am making a program about stack, but everytime I enter a case choice, it loops the number i entered. Why so?

example : Enter your choice: 1 1 1 1 1 1 1 1 1 1- it doesnt stop asking

void display();
void push();
void pop();
void stackList();
int stack[100];
int top = -1;

int main(){

char ch;
char character; *// user input of char*

    display ();

    printf("\n\nEnter your choice: ");

    do 
    {   
        scanf("%c",&ch); *// enter choice of user* 

         switch(ch)
         {
            case 1: push();      break;
            case 2: pop();       break;
            case 3: stackList(); break; *// display stacks*
         }
     
     }
     while( ch != 'z' || ch != 'Z');
 
  }

this is my push function

 void push ()
    {

    char character;

    printf("\n\npress 'Z' to exit.......");

    if ( top == MAX -1 )
    {
        printf(" OVERFLOW ");
    }

    else
    {
        printf("Enter a character to push:\n");   
        do 
        {   
            scanf("%c",&character); *// asking user for character*
        
            top = top+1;
            stack[top]=character;
        }
     
    while( character != 'z' || character != 'Z');
    printf("\nExiting...");
    
    }   
}

** for example : Enter your choice: 1 1 1 1 1 1 1 1 1 1- it doesnt stop asking **