How to find if all brackets are balanced (C)

Question

So I have an array full of brackets, for example :

1) (()())())((())(())

2) ()((()()))

Any open bracket ( '(' ) should also be closed by another one (')')

So for example 1) ->

(()())())((())(()) -> (....)..)((..)(..) -> ())(()() -> .)(.. , so the answer is no because from here we can see that not all of the brackets are balanced

For example 2) ->

()((()())) -> .((..)) -> (()) -> (..) -> () -> .. , so here the answer is yes because all brackets are balanced. In this case, I would also like to print the positions of all couples of brackets that are balanced, for example :

1,2 & 5,6 & 7,8 & 3,10 & 4,9

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So I tried with a loop that looks for a '(' then another loop inside which tries to find a ')' but I can't delete elements from an array so I am not sure — Nson, Mar 09 '17 at 09:13
Please show your research/debugging effort so far. Please read [Ask] page first. — Sourav Ghosh, Mar 09 '17 at 09:14
that's too broad. Here's a similar Q&A in python: http://stackoverflow.com/questions/42681287/checking-multiple-for-items-in-a-for-loop-python — Jean-François Fabre, Mar 09 '17 at 09:14
*"Deleting elements from array in C is impossible"* - well that statement is just plain wrong — UnholySheep, Mar 09 '17 at 09:15
@Nson first result of a quick google search: http://www.codeforwin.in/2015/07/c-program-to-delete-element-from-array.html — UnholySheep, Mar 09 '17 at 09:17
Too many downvotes yet the question is legit with explainations and I have already told what I've tried so... idk — Nson, Mar 09 '17 at 09:29
I don't understand why anybody would think this question is "too broad", especially when there is already a satisfactory and accepted answer. — JeremyP, Mar 09 '17 at 10:16

Tatsuyuki Ishi · Answer 1 · 2017-03-09T09:32:20.513

In your case, it's as simple using a counter. Increment for (, and decrement for ). It shouldn't go under 0, and should be 0 in the end if balanced.

You may consider using a stack, if you're creating some syntax parser like the compilers and interpreters do.

EDIT: you need to use a stack to print out the pairs. You need to implement a stack by hand in C, so the following is reference code in C++.

std::stack<int> s;
switch(string[i]) {
    case '(':
        s.push(i);
        break;
    case ')':
        if(!s.empty()) {
            printf("%d, %d\n", s.top(), i);
            s.pop();
        } else {
            // Fail here
        }
        break;
}
if(!s.empty()) // Fail here

score 0 · Answer 2 · answered Mar 09 '17 at 09:18

0

Count opening and closing brackets:

const char* it;
int         open_n = 0, close_n = 0;

/* Assume array is zero terminated. 
 * Otherwise condition: 'it != &array[ArraySize]' instead '*it' */

for(it = &array[0]; *it ; ++it) {
    switch( *it ) {
    case '(': open_n += 1; break;
    case ')': if( open_n ) { close_n += 1; break; }
              else         { return false; /* ErrorCloseWithoutOpen */ }
    default: break;
    }
}
return open_n ? false : true;

answered Mar 09 '17 at 09:18

Frank-Rene Schäfer

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Your code doesn't fail when the closing bracket precede opening one. – Tatsuyuki Ishi Mar 09 '17 at 09:20
I said I wanted to print the combinations as well – Nson Mar 09 '17 at 09:26
The code returns 'false' if ')' occurs and 'open_n' is zero. – Frank-Rene Schäfer Mar 09 '17 at 09:44

How to find if all brackets are balanced (C)

2 Answers2