Finding derivative of a function stored in a character array

Question

What I need to do is read a file which contains equations. I need to take the derivative of each equation and then write those derivative equations in a different .txt file. I\'

Answer 1

This function will parse the text, cut it in to different parts identified by type[i], stores in a structure. It recognizes x, +, -, and numbers. It can be expand it to include other operators etc.

#define maxlen 50

#define idx         0 //X variable
#define idnumber    1 //number
#define idplus      2 //+ sign
#define idminus     3 //- sign

struct foo
{
    int type[10];//each type can be a number (idnum), +, -, etc.
    int num[10];//if type[i] is number then num[i] identifies that number
    int count;//total number of parts
};

void parse_one_line(struct foo *v, const char *s)
{
    char buf[maxlen];
    memset(buf, 0, maxlen);
    int j = 0;
    //remove white spaces
    for (int i = 0, len = strlen(s); i < len; i++)
    {
        if (s[i] == ' ') continue;
        buf[j] = s[i];
        j++;
    }

    char part[maxlen];
    v->count = 0;
    for (int i = 0, len = strlen(buf); i < len; i++)
    {
        char c = buf[i];
        if (c == 'x')
        {
            v->type[v->count] = idx;
            v->count++;
        }
        else if (c == '+')
        {
            v->type[v->count] = idplus;
            v->count++;
        }
        else if (c == '-')
        {
            v->type[v->count] = idminus;
            v->count++;
        }
        else if (c >= '0' && c <= '9')
        {
            int j = 0;
            memset(part, 0, maxlen);
            for (; i < len; i++)
            {
                c = buf[i];
                if (c >= '0' && c <= '9')
                {
                    part[j] = c;
                    j++;
                }
                else
                {
                    break;
                }
            }
            i--;
            v->num[v->count] = atoi(part);
            v->type[v->count] = idnumber;
            v->count++;
        }
    }
    for (int i = 0; i < v->count; i++)
    {
        switch (v->type[i])
        {
        case idnumber: printf("%d", v->num[i]); break;
        case idx: printf("X"); break;
        case idplus: printf("+"); break;
        case idminus: printf("-"); break;
        default:break;
        }
    }
    printf("\n");
}

int main()
{
    struct foo st;
    parse_one_line(&st, "-23x + 2 + 2x - 3");
    return 0;
}