string expresion C++

vbx_wx · 10-14-2010, 02:36 PM

Hello,i have the following code:

Code:

string s = "1234";
stack<int> st;
for(unsigned int i = 0; i < s.size(); i++)
{
   st.push(atoi(&s[i]));
}

I want to push in to a stack every character in s as an INT,but my code how its writen pushes 1234 then 234 then 34 then 4...how can i modify it to push 1 than 2,3,4 ....Thanx in advance.

Sergei Steshenko · 10-14-2010, 02:46 PM

Quote:

Originally Posted by vbx_wx

Hello,i have the following code:

Code:

string s = "1234";
stack<int> st;
for(unsigned int i = 0; i < s.size(); i++)
{
   st.push(atoi(&s[i]));
}

I want to push in to a stack every character in s as an INT,but my code how its writen pushes 1234 then 234 then 34 then 4...how can i modify it to push 1 than 2,3,4 ....Thanx in advance.

Your code does the right thing - 'atoi' expects a null-terminated string and your code works the way it works exactly for this reason.

You need a temporary null-terminated string holding just one ASCII digit to achieve the code beahvior you want.

vbx_wx · 10-14-2010, 03:35 PM

ok,i made the correction,my next question is: if i have string s = "123 324 546" i want to push iinto the stack 123 then 324 then 546 and not 1 2 3 3 2 4 5 4 6 ? How can it be done ?

tuxdev · 10-14-2010, 03:53 PM

Use stringstreams.

Something smells like homework here. Tell us what the real problem is.

vbx_wx · 10-14-2010, 04:08 PM

Is not homework,just doing exercises from The C++ Programming Language Special,still don`t know why it matters what it is....i need to calculate a string expresion like:

Code:

string s = "122+21-45-11*2*4";

I used Reverse Polish notation but my eproblem only works with numbers from 0-9

Sergei Steshenko · 10-14-2010, 08:27 PM

Quote:

Originally Posted by vbx_wx

Is not homework,just doing exercises from The C++ Programming Language Special,still don`t know why it matters what it is....i need to calculate a string expresion like:

Code:

string s = "122+21-45-11*2*4";

I used Reverse Polish notation but my eproblem only works with numbers from 0-9

Without seeing the code it's impossible to say what's wrong.

Jerry Mcguire · 10-14-2010, 11:21 PM

Your problem is to evaluate an arbituary simple mathematic expression, right?

Start your value stack with 0 as the first item, because a empty expression evaluates to 0, if you agree.

Start your operator stack with '+' as the operator, because an expression like "100" evaluates to 100, which is to be added to the 0 in the value stack.

Scan through your expression, decide what to do when which operator is encountered.

Do everything with pencil and paper first, you will find you way through.