Pass by reference in a stack - c

Question

I am trying to create a simple program where the idea of the task is to create a stack that can take in a set number of values for the array and be able to push and pop the values on command. I am having trouble getting to my pass around correctly. I do not think the values are even getting added to the array.
#include <stdio.h>
#include <stdlib.h>
int push(int x, int st, int stack1[]);
int pop(int st, int stack1[]);
int main ()
{
char stack1[10];
int stmax = 5;
int st = -1;
int x;
int choice;
while (1) {
printf("What would you like to do? \n1. Check Empty\n2. Check Full\n3. Push\n4. Pop\n5. show\n\n");
scanf("%d", &choice);
switch (choice) {
case 1:
if(st = -1){
printf("Empty\n");
} else {
printf("Not Full\n");
}
break;
case 2:
if(st == stmax) {
printf("Full\n");
} else {
printf("Not Full\n");
}
break;
case 3:
printf("Enter a int to add to the stack:\n");
scanf("%d", &x);
push(x, st, stack1);
break;
case 4:
pop(st, stack1);
printf("%d", stack1[st]);
default:
break;
}
} return(0);
}
int pop(int st, int stack1[]) {
int data;
data = stack1[st];
printf("%d", data);
return(st);
}
int push(int x, int st, int stack1[]) {
st ++;
stack1[st]=x;
return(st);
}