#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <stdbool.h>
#include <ctype.h>

struct stack{
    char data[100];
    int size;
}s;

void push(char ch){
    if(s.size < 100){
        s.size++;
        s.data[s.size] = ch;
    }
    else
        exit(0);
} 

char pop(){
    if(s.size > 0){
        s.size--;
        return (s.data[s.size]);
    }
    else 
        exit(0);
}

bool find_pair(char a, char b){
    if(a == '(' && b == ')') 
        return true;
    if(a == '{' && b == '}')
        return true;
    if(a == '<' && b == '>')
        return true;
    if(a == '[' && b == ']')
        return true;

    return false;

}
char right_pair(char a){
    char b;
    if(a == '(')
        b = ')';
    if(a == '{')
        b = '}';
    if(a == '[')
        b = ']';
    if(a == '<')
        b = '>';

    return b;    
}

char gettop(){
    return s.data[s.size];
}

int main(){
    
    
    char line[100];
    s.size = -1;

    printf("Read: ");
    char *x = fgets(line, 100, stdin);
    printf("%s", line);

    int l = strlen(line);
    int i, j = 0;
    char *a = calloc(l, sizeof(char));
    char *b = calloc(l, sizeof(char));
     
    for(i = 0; i < l; i++){
         //a[i] = gettop();  
        // b[i] = right_pair(a[i]);
  
        if(line[i] == '{' || line[i] == '(' || line[i] == '[' || line[i] == '<'){
            push(line[i]);
            a[j] = gettop();
            b[j] = right_pair(a[j]);
            j++;
            //printf("%c", b[i]);
        }
        if(line[i] == '}' || line[i] == ')' || line[i] == ']' || line[i] == '>'){   
            //a[i] = gettop();
            //b[i] = right_pair(a[i]);
            if(s.size == -1){
                printf("Unexpected closing bracket %c in %d\n", line[i], i);
                return 0; 

            }
            else if(!find_pair(gettop(), line[i])){
                printf("Crossed bracket %c in %d, expected %c\n", line[i], i, b);
                return 0;            
            }
            else{
                 pop();
            }

        }
    }
    i = 0;
    if(s.size == -1){
        printf("All brackets OK\n");
    }
    else {
        printf("Missing closing brackets: %s \n", b);        
    }
    free(a);
    free(b);
    return 0;
}