Mergesort bug + warnings - c

Question

I have the following code, followed it form a tutorial, and it doesn't seem to do anything. I tried debugging it with KDB but I can't find the problem why it doesn't sort.
Maybe someone on here can help me, thanks in advance!
#include <stdio.h>
#include <stdlib.h>
void Mergesort(int *a, int length) {
int i = 0;
int mid = 0;
int *L, *R;
mid = length / 2;
if (length < 2)
return;
else {
L = (int*)malloc(sizeof(int) * mid);
R = (int*)malloc(sizeof(int) * (length - mid));
for (i = 0; i < mid; i++) {
L[i] = a[i];
}
for (i = mid; i < length; i++) {
R[i - mid] = a[i];
}
Mergesort(L, mid);
Mergesort(R, length - mid);
Merge(a, L, R, length);
}
}
void Merge(int *a, int *L, int *R, int length) {
int i = 0, j = 0, k = 0;
int mL, mR;
mL = length / 2;
mR = length - mL;
while (i < mL && j < mR) {
if (L[i] < R[j]) {
a[k] = L[i];
i++;
} else {
a[k] = R[j];
j++;
}
k++;
}
while (i < mL) {
a[k] = L[i];
i++;
k++;
}
while (j < mR) {
a[k] = R[j];
i++;
k++;
}
}
void main() {
int a[7] = { 5, 4, 99, 13, 34, 54, 2 };
int u = 0;
Mergesort(a, 7); // call to Mergesort
for (u = 0; u < 7; u++) {
printf(" %d\t", a[u]);
}
printf("\n\n\n");
}
I would really appreciate it since I need to understand it before Thursday next week :P

Answer 1

Here you're incrementing i but you should increment j in Merge function.
while(j<mR)
{
a[k]=R[j];
j++;
k++;
}
Edit:
put function declation after the header files void Merge(int *a,int *L,int *R,int length); otherwise you will get implicit declaration of function ‘Merge’ warning.
#include<stdio.h>
#include<stdlib.h>
void Merge(int *a,int *L,int *R,int length);
//rest of your code