How to make my program only check inside parenthesis?

Question

The goal of the program is to be able to extract integers in a string(char), only if they are inside a set of parenthesis. I am also suppose to print out an error message if the string doesn't meet these requirements.

For example: char str = "( 1 2 3)"; this would print that it found integers 1, 2, and 3. But lets say str was char str = " 1 2 3( 4 5 6); would return a call to my error function because it has bad formatting. If the string contains anything else that is not a number or white space it should print error also. Lastly it is suppose to check looking inside the parenthesis until it finds the end parenthesis.

At the moment, I can search thru any string and extract the integers but I cannot figure out how to determine if there are anything else besides numbers and check only inside parenthesis.

void scanlist(char *str)
{
    char *p = str;
    while (*p) {
    if ((*p == '-' && isdigit(p[1])) || (isdigit(*p))) {
        int val = strtol(p, &p, 10);
        on_int(val);
    }
    else {
        p++;
    }

}

I have tried putting another if statement after the while seeing if it starts with a '(' but it doesn't do anything. Please and thanks!

Answer 1

Hope this helps

int main()
    {
        //variable declerations
        int j = 0;
        // str is the string that is to be scanned for numbers
        string  str= "(123)";
        //iterator to point at individual characters in a string 
        //It starts at the beginning of a string
        //a string is an array of characters
        string::iterator p = str.begin();
        //if the iterator that i named p does not find the bracket at the begining 
        //prints out an error massage
        if(*p != '(')
        {
            cout<<"error";
        }
        //else if it finds a bracket at the begining goes into the loop
        // I use *p to veiw the content that the iterator points to 
        // if you only use p you will get the address which is a bunch of wierd numbers like A0Bd5 
        if(*p == '(')
        {
            //while loop to move the iterator p one caracter at a time until reach end of string
            while(p != str.end())
            {
                       // if end bracket is reached end loop
                       if(*p == ')')
                       {
                       break;
                       }
                //if it finds a digit prints out the digit as character not as int! 
                if(isdigit(*p))
                {

                    cout<<*p<<endl;
                }
                //increments the iterator by one until loop reach end of string it breaks
                p++;
            }
        }

        //to pause the screen and view results
        cin.get();

    }

Answer 2

You need to hold some state regarding your position. For example:

int inside_paren = 0;
while (*p) {
    switch (*p) {
    case '(':
        if (inside_paren)
            /* error */
        inside_paren = 1;
        break;
    case ')':
        /* ... */
        inside_paren = 0;
        break;
    default:
        if (!isdigit(*p) || !inside_paren)
            /* error */
    }
}