Fixed bug of invalid s.d; also migrated to use std:: instead of using…

… namespace sts.

Note the comments are migrated to the header.

random_price.cpp

@@ -4,47 +4,37 @@
 #include <iostream>
 #include <random>
 
-using namespace std;
-
 double init_stock_price(int a){
-	//Stock prices cluster in 3 tiers in our world: about 5 hkd (a=1) 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). 
-	//If an invalid input we default a=1.
-    	std::random_device rd;
-	//std mt19937 Merssane Twister
+	std::random_device rd;
+	//Merssane Twister
 	std::mt19937 gen(rd());
-	//normal_distribution<double> distribution(5.0, 2.0);
 	if(a==2){
-		normal_distribution<double> distribution(50.0, 20.0);
+		std::normal_distribution<double> distribution(50.0, 20.0);
 		return distribution(gen);
-		}
+	}
 	else {
 		if(a==3){
-		normal_distribution<double> distribution(150.0, 50.0);
+		std::normal_distribution<double> distribution(150.0, 50.0);
 		return distribution(gen);
 		}
 	else{
-		normal_distribution<double> distribution(5.0, 2.0);
+		std::normal_distribution<double> distribution(5.0, 2.0);
 		return distribution(gen);
 		}
 		}
     return 0.0;
 }
 double random_sd(float price){
-	//s.d. usually 1%-5% of initial stock price; modelling with normal(0.03*init_price, 0.02*init_price)
 	std::random_device rd;
 	std::mt19937 gen(rd());
-	normal_distribution<double> d(0.03*price, 0.02*price);
-	return d(gen);
+	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){
-	//upper_limit and lower_limit are FRACTIONS of the mean so that it remains usable even for a rise 
-	// or fall of large margin; unless changed manually. e.g. a 3% of the mean lower limit 
-	//until mean price fall then lower_limit=0.03
 	std::random_device rd;
-    std::mt19937 gen(rd());
-	normal_distribution<double> distribution(mean, sd);
+   	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)){
@@ -58,6 +48,5 @@ double random_stock(float &mean, float &sd,float &upper_limit, float &lower_limi
 	return price;
 }
 unsigned int random_integer(unsigned int max_integer) {
-    // Return a random integer from 0 to max - 1
-    return rand() % max_integer;
+	return rand() % max_integer;
 }