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#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
 
// A structure to represent a stack
struct Stack {
    int top;
    unsigned capacity;
    int* array;
};
 
// function to create a stack of given capacity. It initializes size of
// stack as 0
struct Stack* createStack(unsigned capacity)
{
    struct Stack* stack = (struct Stack*)malloc(sizeof(struct Stack));
    stack->capacity = capacity;
    stack->top = -1;
    stack->array = (int*)malloc(stack->capacity * sizeof(int));
    return stack;
}
 
// Stack is full when top is equal to the last index
int isFull(struct Stack* stack)
{
    return stack->top == stack->capacity - 1;
}
 
// Stack is empty when top is equal to -1
int isEmpty(struct Stack* stack)
{
    return stack->top == -1;
}
 
// Function to add an item to stack.  It increases top by 1
void push(struct Stack* stack, int item)
{
    if (isFull(stack))
        return;
    stack->array[++stack->top] = item;
    printf("%d pushed to stack\n", item);
}
 
// Function to remove an item from stack.  It decreases top by 1
int pop(struct Stack* stack)
{
    if (isEmpty(stack))
        return INT_MIN;
    return stack->array[stack->top--];
}
 
// Function to return the top from stack without removing it
int peek(struct Stack* stack)
{
    if (isEmpty(stack))
        return INT_MIN;
    return stack->array[stack->top];
}
 
// Driver program to test above functions
int main()
{
    struct Stack* stack = createStack(100);
    char exp[100];
    int a, b;

    printf("Enter a valid postfixed expression (each number can be a positive digit only): ");
    scanf("%s", exp);

    for(int i = 0; i < strlen(exp); i++) {
        switch(expr[i]) {
            case '+':
                a = pop();
                b = pop();
                push(a + b);
            case '-': 
                a = pop();
                b = pop();
                push(a - b);
        }
    }

    getch();
    return 0;
}