So I am tasked with doing the following:

I am given two arrays with a sentinel value. I need to create a function that will iterate through these, finds the GCD of the corresponding elements (ex: array1[0] and array2[0]), and store the result into a result array until it hits the sentinel value.

I already have the part done where it calculates the GCD but I am a little stuck on the iteration part. Here's what I have so far:

#include <stdio.h>

int GCD(int array1[], int array2[]);

int main(void) {
 int array1[] = {245,  92, 16,  1,   3, 22, 255}; 
int array2[] = {57,  226, 240, 15,  22,  3, 255};

int result = GCD(array1, array2);

printf("%d\n", result);
    
return 0;
}

int GCD(int array1[], int array2[]) {

int tempvar1;
int tempvar2;
int result;
int remainder;
int i;
// this part is where I need help iterating
tempvar1 = array1[0];
tempvar2 = array2[0];
remainder = tempvar1;

// this part calculates the GCD
        while (remainder > 0) {
    
                remainder = tempvar1;
            
                while (remainder >= tempvar2) {
                        remainder = remainder - tempvar2;
                    }
            
                tempvar1 = tempvar2;
                tempvar2 = remainder;
            }
    // end GCD calculation 

result = tempvar1;

return result;
}

So far this just calculates the GCD of the numbers in the 0th element but I need it to calculate the GCD for every pair of elements and store them in a result array.

I have tried the 0th element and it works.

CodePudding user response：

Recursive gcd() is faster.

#include <stdio.h>

int gcd (int p, int q) { // Recursive
    if (q) return gcd (q, p % q);
    return p;
}

void GCD_array (int a1[], int a2[], int count, int ans[]) {
    for (int ni = 0; ni < count;   ni)
        ans[ni] = gcd (a1[ni], a2[ni]);
}

int main (void) {
    int array1[] = {245,  92, 16,  1,   3, 22, 255};
    int array2[] = {57,  226, 240, 15,  22,  3, 255};
    int ans [24];
    int count =  sizeof (array1) / sizeof (int);
    GCD_array (array1, array2, count, ans);
    for (int ai = 0; ai < count;   ai)
        printf ("gcd (%d, %d) = %d\n", array1[ai], array2[ai], ans[ai]);

    return 0;
}

CodePudding user response：

Modify GCD as shown to accept two integers

int GCD(int var1, int var2) {
int tempvar1;
int tempvar2;
int result;
int remainder;
int i;

tempvar1 = var1;
tempvar2 = var2;

In the main, add code to loop through the arrays

 int i = 0;
 int array_len = sizeof(array1)/4;
 
 int array_result[array_len];
 
 for (i = 0; i < array_len;   i )
 {
    array_result[i] = GCD(array1[i], array2[i]);
    printf("%d\n", array_result[i]);    
 }

CodePudding user response：

There are few things could be mentioned & improved from your implementation/code:

1. using minus to get the effect of division/modulo.

       while (remainder >= tempvar2) {
           remainder = remainder - tempvar2;
       }

2. your iterations are to check single element only, outer loop stopped when remainder become negative value.

tempvar1 = array1[0];
tempvar2 = array2[0];

/*
if your code are logically correct and returning the correct value, 
you could put more loop, 
to replace the tempvar1 and tempvar2 for checking next pair of single element.
*/

3. your function written to return single int value & what would return in function is also a single int value.

int GCD(int array1[], int array2[]) {

//...ur implementation

result = tempvar1;

return result;
}

FYI, language C has no way to return an array, but to return address of an array. This is applicable when result changed to array-type variable, feel free to explore more at here: In C,how do I make this program return the address of an array,instead of address of first element?