0

I tried to split string into 3 parts but its not working properly. i need it to be split by + and - and =.

int main() {

double a, b, c, x, x1, x2, d;

string str, part1, part2, part3, avand, miand, azand;

str = "2+4x-2x^2=0";
size_t count = count_if(str.begin(), str.end(), [](char c) {return c == 'x'; });

if (count == 2) {
    int i = 0;
    while (str[i] != '+' && str[i] != '-') {
        part1 = part1 + str[i];
        i++;
    }
    while (str[i] != '+' && str[i] != '=') {
        part2 = part2 + str[i];
        i++;
    }
    i++;
    for (i; i < str.length(); i++) {
        part3 = part3 + str[i];
    }
  }
}
Improve this question
6
  • 1
    std::string::find_first_of should be astoundingly helpful. Here's a demonstration of it in action Commented Oct 19, 2022 at 22:19
  • Side note: You should state exactly what you want out for the given input. Commented Oct 19, 2022 at 22:20
  • for example i have 1+2+3 as user input string, i just want them to split a=1, b = 2,c =3. but i dont know what it can be, maybe it has 6 numbers in one part so i cant substr it Commented Oct 19, 2022 at 22:22
  • Groovy. The demonstration linked above should do almost exactly what you want. I recommend replacing part1, part2 and part3 with an array or a vector like in the demonstration because when you have sequentially named or numbered variables, using a loop and a container is almost always easier (and easier to expand when the teacher says, "Now do it with 4 parts!"). Commented Oct 19, 2022 at 22:30
  • @EduardAtoyan If you though outside the box, you could have replaced +, - and = with spaces, and then simply use std::istringstream to get the parts. No need for tricky (and error prone) logic finding spaces, etc. Commented Oct 19, 2022 at 22:40

2 Answers 2

Reset to default
1

Not knowing exactly what you are trying to accomplish, I am assuming you simply want to get the expressions that fall between the +, - and the =.

If so, since the characters you want to split the string on are +, - and =, another solution is to replace those characters with a single delimiter (a space for example), and then use std::istringstream to get the parts of the string that are remaining:

#include <sstream>
#include <string>
#include <iostream>
#include <vector>

int main() 
{
   std::string str = "2+4x-2x^2=0";
   std::vector<std::string> parts;

   // replace the delimiters with spaces 
   for ( auto& ch : str)
   {
       if ( ch == '+' || ch == '-' || ch == '=')
          ch = ' ';
   }

   // use std::istringstream to parse the new string
   std::istringstream strm(str);
   std::string part;
   while (strm >> part)
      parts.push_back(part);

    // Output values
    for (auto& s : parts)
       std::cout << s << "\n";
}

Output:

2
4x
2x^2
0

Note that I use std::vector to store the parts as they are detected.

Improve this answer
Sign up to request clarification or add additional context in comments.

9 Comments

How can i declare every part separately to string, for example part1=2; part2=4x; and so on
@EduardAtoyan See: Note that I use std::vector to store the parts as they are detected. -- There is nothing more to declare. parts[0] is the first part, parts[1] is the second part, etc. Look how the output loop is designed -- you don't see 4 separate variables, but instead one variable parts that stores all 4 entities.
What if it is -2x, how to make it take - with it into string?
@EduardAtoyan What if it is -2x, how to make it take - with it into string? -- Well, if your goal is to parse this mathematical expression to this extent, then your original approach is ill-advised. It takes much more sophisitication than what you may believe. I was going to comment in the main section that the approach you're taking will only work for certain formatted expressions. If you want something more general, you need to write a formal parser. The answer I gave assumes that all you need to do is use the -, +, and = characters as delimiters.
Just to add, the answer given is nothing more than a simpler way of what you were trying to do. In no way should it be used, again, if your intent was to actually use this to solve a mathematical expression or similar. You have to write a parser, i.e. break up the input into tokens, lexical analysis, etc. For example, what if the ^2 term is the first one instead of the last?
|
0

You need to add a i++; after the first while loop to pass the '+', other wise the code won't enter the second while loop.

Also try to use stringstream to parse the sentence for general purpose. How to use stringstream to separate comma separated strings

Improve this answer

1 Comment

still doesnt work as i needed. you can check it yourself

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.