public static int EvaluateExpression(string expr)
{
if (expr == null || expr.Length == 0)
{
Console.WriteLine("Expression is null or empty");
throw new Exception("Expression is null or empty");
}
GenericStack <int> stack = new GenericStack <int>();
for (int i = 0; i < expr.Length; i++)
{
char ch = expr[i];
int ascii = ch - '0';
if (ascii >= 0 && ascii <= 9)
{
stack.Push(ascii);
}
else if (ch == '*')
{
if (stack.StackCount == 0)
{
Console.WriteLine("Expression invalid");
throw new Exception("Expression invalid");
}
int prevNum = stack.Pop();
int nextNum = expr[i + 1] - '0';
if (nextNum < 0 && nextNum > 9)
{
Console.WriteLine("Expression invalid");
throw new Exception("Expression invalid");
}
stack.Push(prevNum * nextNum);
i++;
}
}
var sum = 0;
while (stack.StackCount > 0)
{
sum = sum + stack.Pop();
}
return(sum);
}
public static string CheckMissingParanthesis(string expr)
{
GenericStack<char> stack = new GenericStack<char>();
if (expr== null || expr.Length == 0) {
return "";
}
// PUsh if you see a opening bracket to the stack
// Pop if you see a closing bracket from the stack
// If the stack is empty when you encounter a closing bracket, it means that there is a missing opening paranthesis
// At the end, if the stack is not empty, then it means that there is a missing closing bracket.
string missingParanthesis = "";
for (int i=0; i<expr.Length; i++)
{
char ch = expr[i];
if (ch == '(')
{
stack.Push(ch);
}
else if (ch == ')')
{
if (stack.StackCount > 0 && stack.Top() == '(')
{
stack.Pop();
}
else
{
missingParanthesis = missingParanthesis + "(\t";
}
}
}
if (stack.StackCount > 0)
{
while (stack.StackCount != 0)
{
char ch = stack.Pop();
if (ch == '(')
{
missingParanthesis = missingParanthesis + ")\t";
}
}
}
return missingParanthesis;
()((()())))))
}