backup.txt

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

void dec_str_add(char *dest, char *num1, char *num2, int length);
char* dec_str_mult(char* num1, char* num2, int length);
void init_num(char* dest, char* origin, int numlength, int origin_length);
void empty_num_arr(char* arr, int numlength);
void num_with_offset(char* dest, int num, int offset);

int main() {
    int numlength = 6;
    char num1[numlength];
    char num2[numlength];
    char num1neg = 0;
    char num2neg = 0;
    init_num(num1, "321", numlength, 3);
    init_num(num2, "321", numlength, 3);
    dec_str_mult(num1, num2, numlength);
}

void string_to_num(char* dest, char* origin, int numlength, int origin_length){
    for(int i = origin_length; i < numlength; i++){
        dest[i] = 0;
    }
    for(int i = 0; i < origin_length; i++){
        dest[i] = origin[origin_length - i - 1] - 48;
    }
}

void empty_num_arr(char* arr, int numlength){
    for(int i = 0; i < numlength; i++){
        arr[i] = 0;
    }
}

void num_with_offset(char* dest, int num, int offset){
    //Only works for num < 100 and at positions in bounds
    dest[offset] = num % 10;
    dest[offset + 1] = num / 10;
}

void dec_str_add(char *dest, char *num1, char *num2, int length) {
    //Addiert beide Werte, ignoriert jeweils die "erste" Stelle
    char zwischenspeicher[length];
    for(int i = 0; i < length; i++){
        zwischenspeicher[i] = 0;
    }

    for(int i = 0; i < length - 1; i++){
        int erg = num1[i] + num2[i] + zwischenspeicher[i];
        zwischenspeicher[i] = erg % 10;
        zwischenspeicher[i + 1] = erg / 10;
    }

    for(int i = 0; i < length; i++){
        dest[i] = zwischenspeicher[i];
    }
}

char* decimal_mult(char* num1, char* num2, int length){
    //Multipliziert zwei Zahlen. Ignoriert jeweils "erste" Hälfte der Zahlen
    char zwischenspeicher[length];
    empty_num_arr(zwischenspeicher, length);

    for(int i = 0; i < length / 2; i++){
        for (int j = 0; j < length / 2; j++) {
            char temp[length];
            empty_num_arr(temp, length);
            num_with_offset(temp, num1[i]*num2[j], i+j);
            decimal_add(zwischenspeicher, zwischenspeicher, temp, length);
        }
    }
    printf("test");
    return zwischenspeicher;
}