Stack

Here's the logic for this program, and some test expressions, in the form of a console application:

using System;

using System.Collections.Generic;

struct CharIndex

{

public readonly char Character;

public readonly int Index;

public CharIndex(char c, int i)

{

Character = c;

Index = i;

}

class Test

{

static void Main()

{

string [] expressions =

{

"a[b] - (c + d)",

"{(a + (b + c)) + (d - e[f])}",

"{(a + (b + c)) + (d - e[f])",

"a + ((b + c[d])",

"a[b] + (c - d)}",

"(a + b)) - (c[d] + e)"

};

foreach(string expression in expressions)

{

Console.WriteLine(expression);

bool balanced = CheckParentheses(expression);

if(!balanced) Console.WriteLine("The parentheses are balanced");

Console.WriteLine();

}

Console.ReadKey();

}

static bool CheckParentheses(string expression)

{

var s = new Stack();

bool unbalanced = false;

for(int i = 0; i < expression.Length; i++)

{

char c = expression[i];

if (c == '(' || c == '[' || c =='{') // push opening parentheses onto stack

{

s.Push(new CharIndex(c, i));

}

else if (c == ')' || c ==']' || c =='}') // check for matching opening parenthesis

{

if (s.Count > 0) // if there are any opening parentheses on the stack

{

CharIndex ci = s.Pop();

if ((c == ')' && ci.Character != '(') ||

(c == ']' && ci.Character != '[') ||

(c == '}' && ci.Character != '{'))

{

Console.WriteLine("'{0}' is unbalanced at index {1}", ci.Character, ci.Index);

unbalanced = true;

}

else // it's an unbalanced closing parenthesis

{

Console.WriteLine("'{0}' is unbalanced at index {1}", c, i);

unbalanced = true;

}

while(s.Count > 0) // any remaining opening parentheses on stack must be unbalanced

{

CharIndex ci = s.Pop();

Console.WriteLine("'{0}' is unbalanced at index {1}", ci.Character, ci.Index);

unbalanced = true;

}

return unbalanced;

}

}

The output should be:

a[b] - (c + d)

The parentheses are balanced

{(a + (b + c)) + (d - e[f])}

The parentheses are balanced

{(a + (b + c)) + (d - e[f])

'{' is unbalanced at index 0

a + ((b + c[d])

'(' is unbalanced at index 4

a[b] + (c - d)}

'}' is unbalanced at index 14

(a + b)) - (c[d] + e)

')' is unbalanced at index 7

I leave it to you to incorporate the logic into a windows forms application.

If you need to highlight something, then you'll need to use a RichTextBox rather than an ordinary TextBox for the user to enter an expression.

1 Reply

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Vulpes13y ago
Here's the logic for this program, and some test expressions, in the form of a console application:

using System;
using System.Collections.Generic;

struct CharIndex
{
public readonly char Character;
public readonly int Index;

public CharIndex(char c, int i)
{
Character = c;
Index = i;
}
}

class Test
{
static void Main()
{
string [] expressions =
{
"a[b] - (c + d)",
"{(a + (b + c)) + (d - e[f])}",
"{(a + (b + c)) + (d - e[f])",
"a + ((b + c[d])",
"a[b] + (c - d)}",
"(a + b)) - (c[d] + e)"
};

foreach(string expression in expressions)
{
Console.WriteLine(expression);
bool balanced = CheckParentheses(expression);
if(!balanced) Console.WriteLine("The parentheses are balanced");
Console.WriteLine();
}

Console.ReadKey();
}

static bool CheckParentheses(string expression)
{
var s = new Stack();
bool unbalanced = false;

for(int i = 0; i < expression.Length; i++)
{
char c = expression[i];
if (c == '(' || c == '[' || c =='{') // push opening parentheses onto stack
{
s.Push(new CharIndex(c, i));
}
else if (c == ')' || c ==']' || c =='}') // check for matching opening parenthesis
{
if (s.Count > 0) // if there are any opening parentheses on the stack
{
CharIndex ci = s.Pop();
if ((c == ')' && ci.Character != '(') ||
(c == ']' && ci.Character != '[') ||
(c == '}' && ci.Character != '{'))
{
Console.WriteLine("'{0}' is unbalanced at index {1}", ci.Character, ci.Index);
unbalanced = true;
}
}
else // it's an unbalanced closing parenthesis
{
Console.WriteLine("'{0}' is unbalanced at index {1}", c, i);
unbalanced = true;
}
}
}

while(s.Count > 0) // any remaining opening parentheses on stack must be unbalanced
{
CharIndex ci = s.Pop();
Console.WriteLine("'{0}' is unbalanced at index {1}", ci.Character, ci.Index);
unbalanced = true;
}

return unbalanced;
}
}

The output should be:

a[b] - (c + d)
The parentheses are balanced

{(a + (b + c)) + (d - e[f])}
The parentheses are balanced

{(a + (b + c)) + (d - e[f])
'{' is unbalanced at index 0

a + ((b + c[d])
'(' is unbalanced at index 4

a[b] + (c - d)}
'}' is unbalanced at index 14

(a + b)) - (c[d] + e)
')' is unbalanced at index 7

I leave it to you to incorporate the logic into a windows forms application.

If you need to highlight something, then you'll need to use a RichTextBox rather than an ordinary TextBox for the user to enter an expression.