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I'm still a student in C. I need to do a practical task for this semester but I can't. I've tried everything, but it doesn't seems to work. What I need to do is to create a fractal which is a figure just like this one:

enter image description here.

Fractals are never-ending patterns. I need to create one by using certain commands, like F, - and +. F means forward, - means to turn left and + to turn right, or vice versa. First the program reads the base pattern, which is F. Then it needs to replace it by another constant pattern: 'F-F+F+FF-F-F+F'. After that, other figure is created, because the commands were replaced. So, iit functions like this: every time it finds a 'F', this 'F' is replaced by 'F-F+F+FF-F-F+F'. The - and + are kept in the same spot.

I need to do this in C language (can't be in c++). I created this function using arrays and pointers. Char v[] is the array received to be replaced; int n is its size; char regra[] is the constant pattern 'F-F+F+FF-F-F+F'; 'int n_regra' is the size of this pattern. The qnt_v is other function to count the f's, and the qnt_sinais is to count the + and -. These two are for defining the size of the array to be generated in the function. Hope I made myself clear.

I tried using this function only for the first basic pattern 'F'. The function should return F-F+F+FF-F-F+F, but it didn't return anything.

#include <stdio.h>
#include <string.h>

int qnt_f(char* v, int n){
    int f = 0;
    for(int i=0;i<n;i++){
        if(v[i]=='F'){
            f++;
        }
    }
    return f;
}

int qnt_sinais(char* v, int n){
    int s = 0;
    for(int i=0;i<n;i++){
        if(v[i]=='+' ||  v[i]=='-'){
            s++;
        }
    }
    return s;
}

char *fractal(char v[], int n, char regra[], int n_regra){
    int t = ((qnt_f(v, n))*n_regra)+(qnt_sinais(v, n)*2)+1;
    char fractal[t];
    for(int i=1;i<n;i++){
        if(v[i]=='F'){
            strcat(fractal, regra);
        }
        else if(v[i]=='+'){
            char sinal_mais[2] = "+";
            strcat(fractal, sinal_mais);
        }
        else{
            char sinal_menos[2] = "-";
            strcat(fractal, sinal_menos);
        }
    }
    char *f_ptr = fractal;
    return f_ptr;
}


int main(){


    char axioma[2] = "F";
    char regra[15] = "F-F+F+FF-F-F+F";

    printf("%s\n", fractal(axioma, sizeof(axioma), regra, sizeof(regra)));

    return 0;
}
Barmar
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Arthur Araújo Rabelo
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    Are you sure the loop `for(int i=1;i – Some programmer dude Apr 07 '23 at 19:44
  • Also, having the name `fractal` for both the function and a local variable is kind of confusing. The variable `fractal` isn't initialized by the way, so you can't use it as a destination for `strcat` as it doesn't start out with a null-terminated string. And are you sure `t` is enough to fit all data you want to add to the string, including the null-terminator? – Some programmer dude Apr 07 '23 at 19:46
  • You return a pointer to memory on the stack. It is undefined behavior to interact with data through that pointer after the function returns since. You need to allocate memory on the heap (replace `char fractal[t];` with `char *fractal = malloc(t);`) or pass a buffer for the function to use which will outlive the function. – Locke Apr 07 '23 at 19:47
  • Oh, and `char *f_ptr = fractar;` followed by `return f_ptr;`? That pointer you return will become *immediately* invalid, as the life-time of the array ends and it ceases to exist. – Some programmer dude Apr 07 '23 at 19:47

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