diff --git a/C++/Math/SieveofEratosthenes.cpp b/C++/Math/SieveofEratosthenes.cpp
new file mode 100644
index 0000000..eda9a8f
--- /dev/null
+++ b/C++/Math/SieveofEratosthenes.cpp
@@ -0,0 +1,30 @@
+
+// For a given number it will tell all the prime number less than or equal to it.
+
+#include <bits/stdc++.h>
+using namespace std;
+
+void SieveOfEratosthenes(int n)
+{
+	bool sieve[n+1];
+	memset(sieve, true, sizeof(sieve));
+
+	for (int p=2; p*p<=n; p++)
+	{
+		if (sieve[p] == true)
+		{
+
+			for (int i=p*p; i<=n; i += p)
+				sieve[i] = false;
+		}
+	}
+
+	for (int p=2; p<=n; p++) if (sieve[p]) 	cout << p << " ";
+    cout<<"\n";
+}
+int main()
+{
+	int n; cin>>n;
+	SieveOfEratosthenes(n);
+	return 0;
+}
diff --git a/C++/Sort/mergesort.cpp b/C++/Sort/mergesort.cpp
new file mode 100644
index 0000000..c036402
--- /dev/null
+++ b/C++/Sort/mergesort.cpp
@@ -0,0 +1,76 @@
+#include <iostream>
+using namespace std;
+
+void merge(int arr[], int p, int q, int r) {
+
+
+  int n1 = q - p + 1;
+  int n2 = r - q;
+
+  int L[n1], M[n2];
+
+  for (int i = 0; i < n1; i++)
+    L[i] = arr[p + i];
+  for (int j = 0; j < n2; j++)
+    M[j] = arr[q + 1 + j];
+
+
+  int i, j, k;
+  i = 0;
+  j = 0;
+  k = p;
+
+
+  while (i < n1 && j < n2) {
+    if (L[i] <= M[j]) {
+      arr[k] = L[i];
+      i++;
+    } else {
+      arr[k] = M[j];
+      j++;
+    }
+    k++;
+  }
+
+
+  while (i < n1) {
+    arr[k] = L[i];
+    i++;
+    k++;
+  }
+
+  while (j < n2) {
+    arr[k] = M[j];
+    j++;
+    k++;
+  }
+}
+
+
+void mergeSort(int arr[], int l, int r) {
+  if (l < r) {
+
+    int m = l + (r - l) / 2;
+
+    mergeSort(arr, l, m);
+    mergeSort(arr, m + 1, r);
+    merge(arr, l, m, r);
+  }
+}
+
+void printArray(int arr[], int size) {
+  for (int i = 0; i < size; i++)
+    cout << arr[i] << " ";
+  cout << endl;
+}
+
+int main() {
+  int arr[] = {4,8,2,9,7,3,6};
+  int size = sizeof(arr) / sizeof(arr[0]);
+
+  mergeSort(arr, 0, size - 1);
+
+  cout << "Sorted array: \n";
+  printArray(arr, size);
+  return 0;
+}