Subtracting arrays with different size in c [closed] - c

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void function(int first[], int second[], int third[]) {
int i;
for(i=0;i<64;i++) {
third[i] = first[i] - second[i];
}
}
I want to subtract the second array from the first one. The first one contains 32 numbers and the second one has 13 numbers. It works fine for the first 13 numbers. Once the second array "runs out" of elements, I want to use the numbers from the beginning of the second array. So I want to subtract the second array's first element from the 14th element of the first one, and so on... How could I achieve it?

Answer 1

you can use % to get the remainder of the index from length of the array, this way, you can iterate through the second array in a circular way!
I changed your code to do as you asked for
// get the length of array before you pass it to the function like this:
// int second_len = sizeof(second) / sizeof(second[0]);
void function(int first[], int second[], int third[], int second_len) {
int i;
for(i=0;i<64;i++) {
third[i] = first[i] - second[i % second_len];
}
}

Answer 2

The elements of the first and second array are sequences of positive
numbers and they are both closed with -1
You could just do as below.
Maintain two indexes i and j.
Where i will index larger array and j will index smaller array and once smaller array reaches -1 reset the j to 0 and once larger array reaches -1 break the loop.
void function(int first[], int second[], int third[]) {
int i =0,j=0;
for(i=0; i<64 ; i++;j++) {
if(second[j] == -1)
{
j =0; //Reset the j=0 to start from beginning
}
if (first[i] == -1)
{
third[i] = -1; //Terminate third with -1
break; //Break the loop
}
third[i] = first[i] - second[j];
}
}

Answer 3

One option is to add an additional looping variable:
void function(int first[], int second[], int third[],
int first_size, int second_size)
{
int i=0, k=0;
for(i=0; i<first_size; i++) {
third[i] = first[i] - second[k];
k++;
if (k==second_size)
k = 0;
}
}
i tracks the size of the first array and the output like in your program, and k follows the size of the second array and resets whenever the size is reached. Instead of hardcoded array sizes the function now takes two additional arguments: sizes of the first and second arrays.
For future reference, the rest of this code could look like this:
#include <stdio.h>
void print_array(int arr[], int);
void function(int arr_1[], int arr_2[], int arr_3[], int, int);
int main()
{
int arr_1[] = {1,2,3,4,5};
int arr_2[] = {1,2};
int n_1 = sizeof(arr_1)/sizeof(arr_1[0]);
int n_2 = sizeof(arr_2)/sizeof(arr_2[0]);
int arr_out[n_1];
function(arr_1, arr_2, arr_out, n_1, n_2);
print_array(arr_1, n_1);
print_array(arr_2, n_2);
print_array(arr_out, n_1);
return 0;
}
void print_array(int arr[], int n_elem)
{
int i = 0;
for (i=0; i<n_elem; i++)
printf("%d ", arr[i]);
printf("\n");
}
With print_array as a function to avoid repeating the same lines of code for each print.
For the example input, the output will be 0 0 2 2 4.