diff --git a/random_price.cpp b/random_price.cpp
index c55aeed6..2c2b987e 100644
--- a/random_price.cpp
+++ b/random_price.cpp
@@ -1,9 +1,44 @@
 // code related to randomness
-#include <cstdlib>
 #include "random_price.h"
-using namespace std;
+#include <cstdlib>
+#include <iostream>
+#include <random>
 
+double init_stock_price(int price_profile) {
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::normal_distribution<double> distribution(5.0, 2.0);
+    if (price_profile == 2) {
+        distribution.param(std::normal_distribution<double>::param_type(50.0, 20.0));
+    }
+    if (price_profile == 3) {
+        distribution.param(std::normal_distribution<double>::param_type(150.0, 50.0));
+    }
+    return distribution(gen);
+}
+double random_sd(float price) {
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::normal_distribution<double> d(0.03 * price, 0.02 * price);
+    return abs(d(gen));
+}
+double random_stock(float & mean, float & sd, float & upper_limit,
+                    float & lower_limit) {
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::normal_distribution<double> distribution(mean, sd);
+    float price = distribution(gen);
+    // for mean > temp i.e. falling prices
+    if ((mean - price) > (lower_limit * mean)) {
+        mean = price;
+    }
+    // rising prices
+    if ((price - mean) > (upper_limit * mean)) {
+        mean = price;
+    }
+    sd = random_sd(price);
+    return price;
+}
 unsigned int random_integer(unsigned int max_integer) {
-    // Return a random integer from 0 to max - 1
     return rand() % max_integer;
 }
diff --git a/random_price.h b/random_price.h
index 3068a0ea..0e36505e 100644
--- a/random_price.h
+++ b/random_price.h
@@ -1,5 +1,33 @@
 #ifndef RANDOM_PRICE_H
 #define RANDOM_PRICE_H
 
+/**
+#ifndef
+#define are to prevent double include the header
+*/
+
+/**
+ * Initial Stock Price Generator
+ * if price_profile=2 mean 50 sd 20; if price_profile=3 mean 150 sd 50; else mean 5 sd 2;
+ *Stock prices cluster in 3 tiers in our world: about 5 hkd (a=ELSE) variating about 2 hkd; , 50 hkd(a=2) variating about 20 hkd,
+ *and 150 hkd(a=3)variating about 50 hkd (based on a very little sample observation of real world).
+ */
+double init_stock_price(int a);
+/**
+ * Stock Standard Deviation Generator (for both initial and after initial)
+ * s.d. usually 1%-5% of initial stock price;
+ * modelling with absolute value of norm dist mean 0.03*init_price; s.d. 0.02*init_price (yes, s.d. of s.d.)
+ */
+double random_sd(float init_price);
+/**
+ * Random Stock Price Generator (non-initialising)
+ * requires mean, s.d., upper limit increase threshold (FRACTION of mean) and lower limit decrease threshold (FRACTION of mean)
+ * e.g. both 0.03; then the mean changes to exactly the new price if the value differ from mean by 3%
+ */
+double random_stock(float & mean, float & sd, float & upper_limit, float & lower_limit);
+/**
+ * Random integer function in choosing stock type
+ * Return a random integer from 0 to max - 1
+ */
 unsigned int random_integer(unsigned int max_integer);
 #endif