check_nesting.c

#include "stack.h"
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void) {
  int i;
  char input[256], closing;
  fprintf(stderr, "Enter parantheses and/or braces: ");
  // takes all of the input entered by the user and stores it in the character
  // array called input.
  fgets(input, 256, stdin);

  // Iterate through each character of the string stored in input.
  for (i = 0; i < strlen(input) - 1; i++) {
    // if an opening parantheses or brace is encountered, push it to the stack.
    if (input[i] == '(' || input[i] == '{') {
      push(input[i]);
      // if a closing parantheses is encountered, pop the last item from the
      // stack.
    } else if (input[i] == ')') {
      closing = pop();
      // if popped item is a matching opening parantheses, continue iterating,
      // otherwise break from the loop.
      if (closing == '(') {
        continue;
      } else {
        // this is for the case where the last parantheses or braces popped
        // results in an empty stack and a mismatched pair. An empty stack
        // indicates proper nesting and this is not the case, therefore, push
        // the popped item back onto the stack and break from the loop.
        push(closing);
        break;
      }
    } else if (input[i] == '}') {
      closing = pop();
      if (closing == '{') {
        continue;
      } else {
        push(closing);
        break;
      }
    }
  }
  //
  if (is_empty()) {
    printf("Parentheses are nested properly\n");
  } else {
    printf("Parentheses are not nested properly\n");
  }

  return 0;
}