C++: Removing all asterisks from a string where the asterisks are NOT multiplication symbols

Question

So basically, I might have some string that looks like: "hey this is a string * this string is awesome 97 * 3 = 27 * this string is cool".

However, this string might be huge. I'm trying to remove all the asterisks from the string, unless that asterisk appears to represent multiplication. Efficiency is somewhat important here, and I'm having trouble coming up with a good algorithm to remove all the non-multiplication asterisks from this.

In order to determine whether an asterisk is for multiplication, I can obviously just check whether it's sandwiched in between two numbers.

Thus, I was thinking I could do something like (pseudocode):

wasNumber = false
Loop through string
   if number 
      set wasNumber = true
   else
      set wasNumber = false
   if asterisk
      if wasNumber
         if the next word is a number
            do nothing
         else
            remove asterisk
      else
         remove asterisk

However, that^ is ugly and inefficient on a huge string. Can you think of a better way to accomplish this in C++?

Also, how could I actually check whether a word is a number? It's allowed to be a decimal. I know there's a function to check if a character is a number...

Answer 1

Fully functioning code:

#include <iostream>
#include <string>
using namespace std;

string RemoveAllAstericks(string);
void RemoveSingleAsterick(string&, int);
bool IsDigit(char);

int main()
{
    string myString = "hey this is a string * this string is awesome 97 * 3 = 27 * this string is cool";
    string newString = RemoveAllAstericks(myString);

    cout << "Original: " << myString << "\n";
    cout << "Modified: " << newString << endl;

    system("pause");
    return 0;
}

string RemoveAllAstericks(string s)
{
    int len = s.size();
    int pos;

    for(int i = 0; i < len; i++)
    {
       if(s[i] != '*') 
          continue;

       pos = i - 1;
       char cBefore = s[pos];
       while(cBefore == ' ')
       {
          pos--;
          cBefore = s[pos];
       }

       pos = i + 1;
       char cAfter  = s[pos];
       while(cAfter == ' ')
       {
          pos++;
          cAfter = s[pos];
       }

       if( IsDigit(cBefore) && IsDigit(cAfter) )
          RemoveSingleAsterick(s, i);
    }

    return s;
}

void RemoveSingleAsterick(string& s, int i)
{
    s[i] = ' '; // Replaces * with a space, but you can do whatever you want
}

bool IsDigit(char c)
{
   return (c <= 57 && c >= 48);
}

Top level overview:

Code searches the string until it encounters an *. Then, it looks at the first non-whitespace character before AND after the *. If both characters are numeric, the code decides that this is a multiplication operation, and removes the asterick. Otherwise, it is ignored.

See the revision history of this post if you'd like other details.

Important Notes:

• You should seriously consider adding boundary checks on the string (i.e. don't try to access an index that is less than 0 or greater than len
• If you are worried about parentheses, then change the condition that checks for whitespaces to also check for parentheses.
• Checking whether every single character is a number is a bad idea. At the very least, it will require two logical checks (see my IsDigit() function). (My code checks for '*', which is one logical operation.) However, some of the suggestions posted were very poorly thought out. Do not use regular expressions to check if a character is numeric.

Since you mentioned efficiency in your question, and I don't have sufficient rep points to comment on other answers:

A switch statement that checks for '0' '1' '2' ..., means that every character that is NOT a digit, must go through 10 logical operations. With all due respect, please, since chars map to ints, just check the boundaries (char <= '9' && char >= '0')