Command Line Calculator

[xxhashxx]

Hi everyone, i just wanted some advice as to solve my assignment.

i want to write command line calculator that accepts a formula from the user and respond with the calculated result. An example would be:
33.2+2*150/5^2
Which would display:
The answer is : 45.2

So i am considering different things in order to do this:

cin >> user_input ;
int length = user_input.length();
int i;
string array_1[100];
for (i = 0; i<length ; i++)
{
array_1[i] = user_input.substr(i,1);
cout << array_1[i]<< endl;
}


I am placing each character in an array.

I will use "atoi" to convrt char to int , for the calculation
( a problem i face with this is that atoi only accept const char*, how can i resolve this).
And use .find() to give the location of operators (+ - x /).

Do you think that i am heading in the right direction with, this or id there a simple but shorter way?

[jsmith]

atoi() returns an int, which means you cannot enter floating point values.

better would be to use strtod() [string-to-double].

string foo;

foo.c_str() gets you a const char*.

are you honoring operator precedence or just evaluating left to right?

have you learned in class about Reverse Polish Notation?

[xxhashxx]

Thanks jsmith,

Yes i am honoring operator precendence, and am also taking into consideration the use of () brackets in the user input.

I know what the RPN is, but i dont know how to implement it in this case.

I am also working on another method of doing this. So hopefully that works out better.

[jsmith]

It seems to me like implementing RPN would be easier to handle operator precedence and parentheses correctly.

I don't see how using find() to locate the operators would help you; the bottom line is that you have to parse the input left to right.

[eker676]

http://en.wikipedia.org/wiki/Reverse_Polish_notation