My sorting function gives unexpected output - c

Question

I write a generalized C language program that given a sequence of numbers, sorts, even numbers in ascending order, odd numbers in descending order and places all even numbers in the initial part of an array then odd numbers.
Example: 2, 5, 1, 0, 4, 7, 9, 3, -2, 10, 20, 15
Expect: -2, 0, 2, 4, 10, 20, 15, 9, 7, 5, 3, 1
Six functions are required. The solution must be provided using only the mentioned functions.No global variables shall be declared. Use appropriate data types, return types and function arguments.
Input() – takes total number of elements and values as input from the user. Stores the values in “input” array.
SortEven() – sorts the even numbers in ascending order and stores them in an array named “even”
SortOdd() – sorts the odd numbers in descending order and stores them in an array named “odd”
Merge() – places all the even numbers in the initial part of array named “result” then odd numbers.
Display() – displays the contents of “result” array.
main() – calls the Input() module to begin the execution.
Program:
#include <stdio.h>
int main() {
input();
}
int input() {
int n;
printf("Enter The Number Of Elements You Want To Enter : ");
scanf("%d", &n);
int a[n], i, ev = 0, od = 0;
for (i = 0; i < n; i++) {
printf("Enter Number : ");
scanf("%d", &a[i]);
if (a[i] % 2 == 0) {
ev++;
} else {
od++;
}
}
sorteven(a, ev, od, n);
}
int sorteven(int a[], int ev, int od, int n) {
int i, j = 0, swap, even[ev];
for (i = 0; i < n; i++) {
if (a[i] % 2 == 0) {
even[j] = a[i];
j++;
}
}
for (i = 0; i < ev - 1; i++) {
for (j = 0; j < ev - i - 1; j++) {
if (even[j] > even[j + 1]) {
swap = even[j];
even[j] = even[j + 1];
even[j + 1] = swap;
}
}
}
sortodd(a, ev, od, n, even);
}
int sortodd(int a[], int ev, int od, int n, int even[]) {
int i, k = 0, swap, odd[od], j;
for (i = 0; i < n; i++) {
if (a[i] % 2 != 0) {
odd[k] = a[i];
k++;
}
}
for (i = 0; i < od - 1; i++) {
for (j = 0; j < od - i - 1; j++) {
if (odd[j] < odd[j + 1]) {
swap = odd[j];
odd[j] = odd[j + 1];
odd[j + 1] = swap;
}
}
}
merge(a, ev, od, n, even, odd);
}
int merge(int a[], int ev, int od, int n, int even[], int odd[]) {
int merge[n], i;
for (i = 0; i < ev; i++) {
merge[i] = even[i];
}
for (i = ev; i < n; i++) {
merge[i] = odd[i];
}
display(merge, n);
}
int display(int merge[], int n) {
int i;
printf("OUTPUT : ");
for (i = 0; i < n; i++) {
printf(" %d ", merge[i]);
}
}

Answer 1

When looking in the source code, the problem is located in the merge() function.
Both sorteven() and sortodd()are well implemented, but when merging both sub-arrays, the for(i=ev;i<n;i++) is not correct.
To add the odd[] array at the end of the even[] array, write:
int j;
// point to the first item of odd[]
for(i=ev,j=0;i<n;i++,j++)
{
merge[i]=odd[j];
}
Instead of:
only odd[0] to odd[od-1] are allocated and defined.
for(i=ev;i<n;i++)
{
merge[i]=odd[i];
}
Outputs of:
{ 2, 5, 1, 0, 4, 7, 9, 3, -2, 10, 20, 15 };
Are:
OUTPUT : -2 0 2 4 10 20 15 9 7 5 3 1