diff --git a/lesson#5/main.d b/lesson#5/main.d
new file mode 100644
index 0000000..f93bbb3
--- /dev/null
+++ b/lesson#5/main.d
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+//	IMPROVING OUR CALCULATOR
+//	LEARN: functions, while loop, break statement
+
+//	importing writeln, write and readf functions
+import std.stdio: writeln, write, readf;
+
+void main() {
+	float a = 0;
+	float b = 0;
+	char operation; //	'+', '-', '*', '/'
+
+	write("first number: ");
+	readf(" %s", a);
+
+	write("second number: "); 
+	readf(" %s", b);
+
+	write("operation: ");
+
+	/*
+		while(condition is true) { //	if condition is false, it will terminate the loop and continue down below
+			repeat;
+		}
+	*/
+
+	/*
+	bool unknownOperation = true;
+	while(unknownOperation) {
+		readf(" %s", operation);
+
+		if(operation == '+' || operation == '-' || 
+			operation == '*' || operation == '/') {
+			unknownOperation = false;
+		} else {
+			write("Error! Unknown operation. Try again: ");
+		}
+	}
+	*/
+
+	while(true) {
+		readf(" %s", operation);
+
+		if(operation == '+' || operation == '-' || 
+			operation == '*' || operation == '/') {
+			break;
+		} else {
+			write("Error! Unknown operation. Try again: ");
+		}
+	}
+
+	float result = 0;
+	if(operation == '+') {
+		result = addition(a, b);
+	} else if(operation == '-') {
+		result = substraction(a, b);
+	} else if(operation == '*') {
+		result = multiplication(a, b);
+	} else if(operation == '/') {
+		result = division(a, b);
+	}
+
+	writeln(a, operation, b, "=", result);
+
+	//	further instructions...
+}
+
+//	our functions
+
+float addition(float a, float b) {
+	return a+b;
+}
+
+float substraction(float a, float b) {
+	return a-b;
+}
+
+float multiplication(float a, float b) {
+	return a*b;
+}
+
+float division(float a, float b) {
+	return a/b;
+}
+
+/*
+	returnType functionName(parameterList) {
+		instructions;
+	}
+	
+	void
+
+	Example:
+	float addition(float a, float b) {
+		float add = a + b;
+
+		return add;
+	}
+
+	float addition(float a, float b) {
+		return a+b;
+	}
+*/
+
+
+
+
+
+
+