Hello to you all ,

I am required to write a program which gets a Math Expression (without checking it is good) and put in Stack only the Brackets .
Implementation of Stack is One-Way Linked List Only.

Examples for Good/Bad Expressions :
(a*{b+c}-4/x +[e-5]) - GOOD

I have build up a Mechanism which checks for each entered char (other than Enter Key and also using closing brackets such as ) or ] or } at the beginning of Expression) what type of bracket it is and pushes it into a stack (we must use LIFO technique for check legal Expression).

I thought of 2 cases :

first case : for each open bracket there is a closing one so i check top of stack to bottom of stack and carry on till i reach to middle .
second case : what happens if i have this sequence - ()[]{} - meaning i need to check top against the next , and so on (top of stack to bottom of stack will not help in this case)

I kinda stuck on Algorithm Think Phase :-)

Code Added . Any Ideas ?

Thank you , Yotam , Israel

## All 6 Replies

``````The logic should be like this :
while ( input != 13 )
{
if input is '(' or '{' or '[' or ')' or '}' or ']'
{
if input is '(' or '{' or '['
push it into the stack.
else if input is  ')' or '}' or ']'
{
if stack is empty
pop cell from stack
if cell "matches input"
we are ok.
else if cell dont "matches input" or stack is empty
}
}
}
if  the stack is not empty

Also I would suggest replacing your input function
with fgets.
A nice touch would be to add to the switch statment
a default case, checking if it is a number of math experssion.
Don't ever write code like this :

``````free(top);
top=top->next;``````

Once you free(p), dont access it !!!!!!!!!!
It will probaly work, but its wrong, and
also your grade will be like it.

``````The logic should be like this :
while ( input != 13 )
{
if input is '(' or '{' or '[' or ')' or '}' or ']'
{
if input is '(' or '{' or '['
push it into the stack.
else if input is  ')' or '}' or ']'
{
if stack is empty
pop cell from stack
if cell "matches input"
we are ok.
else if cell dont "matches input" or stack is empty
}
}
}
if  the stack is not empty

Also I would suggest replacing your input function
with fgets.
A nice touch would be to add to the switch statment
a default case, checking if it is a number of math experssion.
Don't ever write code like this :

``````free(top);
top=top->next;``````

Once you free(p), dont access it !!!!!!!!!!
It will probaly work, but its wrong, and
also your grade will be like it.

I see your point :-)
i build something , but for some reason , it will state all Expression are OK and i tried to Debug it , and i cant figure what went wrong... Code Added . The check is though ASCII code :
'(' - ')' = 1
'' = 2
'{' - '}' = 2

Thanx

I already told you. Dont do this :

``````free(top);
top=top->next;``````

Its very wrong !!!!!
And still you do it again !!!!

First thing better change input by getche to fgets.

Do you think that this is nessary ???
if ( (temp==')') || (temp==']') || (temp=='}') )
{ printf("\n Bad Expression! Run it Again... \n");

``````case ')': { flag=check(temp[i]);  }
case ']': { flag=check(temp[i]);  }
case '}': { flag=check(temp[i]);  }``````

break statemnts!

If the stack is not empty thats wrong

``````if ( top )
{
printf("Items on the stack\n");
flag = 0;
}``````

You are ignoring the case which pop returns zero.

last thing
'(' - ')' == -1

I already told you. Dont do this :

``````free(top);
top=top->next;``````

Its very wrong !!!!!
And still you do it again !!!!

First thing better change input by getche to fgets.

Do you think that this is nessary ???
if ( (temp==')') || (temp==']') || (temp=='}') )
{ printf("\n Bad Expression! Run it Again... \n");

``````case ')': { flag=check(temp[i]);  }
case ']': { flag=check(temp[i]);  }
case '}': { flag=check(temp[i]);  }``````

break statemnts!

If the stack is not empty thats wrong

``````if ( top )
{
printf("Items on the stack\n");
flag = 0;
}``````

You are ignoring the case which pop returns zero.

last thing
'(' - ')' == -1

A few things :
1. how do you Take off the Top each time if not in that way?
2. Added Break Statements , still causes problems in Expression check ,
each EXP check gets OK ....
3. the If sentence - no Math Exp. starts with backwoards brackets. :-)
4. should i pass into the POP function a Pointer to FLAG ?

Thanx

The proramme was good..n i think output will be perfect..but i am in 3rd semester...it is a little bitdifficult for me to understand..is there any simpler code for this bracket checker.....?????

Hello to you all ,

I am required to write a program which gets a Math Expression (without checking it is good) and put in Stack only the Brackets .
Implementation of Stack is One-Way Linked List Only.

Examples for Good/Bad Expressions :
(a*{b+c}-4/x +[e-5]) - GOOD

I have build up a Mechanism which checks for each entered char (other than Enter Key and also using closing brackets such as ) or ] or } at the beginning of Expression) what type of bracket it is and pushes it into a stack (we must use LIFO technique for check legal Expression).

I thought of 2 cases :

first case : for each open bracket there is a closing one so i check top of stack to bottom of stack and carry on till i reach to middle .
second case : what happens if i have this sequence - ()[]{} - meaning i need to check top against the next , and so on (top of stack to bottom of stack will not help in this case)

I kinda stuck on Algorithm Think Phase :-)

Code Added . Any Ideas ?

Thank you , Yotam , Israel

commented: givemetehcodez, lazy -3

write a c++ program that reads from the user a mathematical expression like:
(3+(4-9) * (3/4) * (3+2))

1. your program should check if the expression is correct
1.1 An expression is correct if:
the parantheses are correctly added and are balanced
examples of not correct expressions can be:
)9+8(
(((8-1)

etc

Assume that the numbers are only one digit ( you can extend your program to read more than one digit numbers as a bonus)

2. If the expression is correct, your program should evaluate the expression and display the result.

hint ( use stacks ( certain types of linked lists ) to solve the problem.

commented: givemetehcodez, lazy - thursday huh? you're screwed unless you start now -3
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