Stack.c

#include<stdio.h>
void push(char element, char stack[], int *top, int stackSize){
 if(*top == -1){
  stack[stackSize - 1] = element;
  *top = stackSize - 1;
 }
 else if(*top == 0){
  printf("The stack is already full. \n");
 }
 else{
  stack[(*top) - 1] = element;
  (*top)--;
 }
}
void pop(char stack[], int *top, int stackSize){
 if(*top == -1){
   printf("The stack is empty. \n");
 }
 else{
  printf("Element popped: %c \n", stack[(*top)]);
  // If the element popped was the last element in the stack
  // then set top to -1 to show that the stack is empty
  if((*top) == stackSize - 1){
    (*top) = -1;
  }
  else{
    (*top)++;
  }
 }
}
int main() {
  int stackSize = 4;
  char stack[stackSize];
  // A negative index shows that the stack is empty
  int top = -1;
  push('a', stack, &top, stackSize);
  printf("Element on top: %c\n", stack[top]);
  push('b',stack, &top, stackSize);
  printf("Element on top: %c\n", stack[top]);
  pop(stack, &top, stackSize);
  printf("Element on top: %c\n", stack[top]);
  pop(stack, &top, stackSize);
  printf("Top: %d\n", top);
  pop(stack, &top, stackSize);
  return 0;
}