Thread: Please help me with parsing numbers form a file

Hi,

I am doing my assignment, I need to parse the coefficient and exponent of each term from the polynomials in a file.

A polynomial in the input file will end with a semicolon ;. In the following example there are 4 polynomials:
x-1;x^8+x^7+x^6+x^5+x^4+x^3+x^2+x+1;2x^2-x+1;-x^3+x;

I am not allowed to use string to read the input, and I have to get them on the fly when I read the file.

Here is my attempt, but get bad results.......

Code:

    ifstream file;
    file.open("1160_term_project_data.txt");
    
    int coef;
    int power;
    char ch;
    
        
    while(!file.eof())
    {
        coef = 0;
        power = 0;
        
        if(isdigit(file.peek()))
            file >> coef;
                
        ch = file.get();
        
        if(ch == '-' && isdigit(file.peek()))
        {
            file >> coef;
            coef *= -1;
            ch = file.get();
        }
                    
        if(ch == '+' && file.peek() == 'x')
            coef = 1;
        else if(ch == '-' && file.peek() == 'x')
            coef = -1;
        else if(ch == 'x')
            {
                if (coef == 0)
                    coef = 1;
                
                if(file.peek() == '^')
                {
                    ch = file.get();
                    file >> power;
                }
                else
                {
                    power = 1;
                }
            }
        
        if(coef != 0)
            cout << "Coefficient: " << coef << " Power: " << power << endl;
        
    }
    
    file.close();

I already tried .get(), .unget(), .peek() in the fstrem library, but still can't get what I want.

Am I on the right track, or is there any other ways to do it? Thx.

You should use boost spirit.