devoalda.gitlab.io/content/en/posts/equation_solver.md

---
author: "Devoalda"
authorEmoji: 🐺
title: "Go - Equation Solver"
date: 2020-07-12T11:20:23+08:00
description: Equation Solver with Go
draft: false
hideToc: false
enableToc: true
enableTocContent: true
tocPosition: inner
tocLevels: ["h1", "h2", "h3"]
tags:
- go
- golang
- script
- programming
series:
- Go
categories:
- Go
image: images/postImages/Formula.png
libraries:
- mathjax
---

# Introduction
This is a simple linear and quadratic equation solver in the terminal done in go.

Equation in the form of $ax + b = cx + d$ *or*  $ax^2 + bx + c = 0$

The program will first ask for type of equation, followed by getting the coefficients of each equation.

# Dependencies
* [Go](https://golang.org/dl/)
Go Modules:
``` Golang
import (
	"fmt"
	"math"
	"os"
	"strconv"
)
```

# Code
Create a new project, and make a new file named `main.go`.
Ensure that project path is in `$GOPATH`, this can be checked in your shell with `echo $GOPATH`

## FloatToString Method
This program uses floating points to allow for fractions and decimal numbers in the calculation. This method converts float to string
```golang
func FloatToString(input_num float64) string {
	// to convert a float number to a string
	return strconv.FormatFloat(input_num, 'f', 3, 64)
}
```
This method will be used throughout the program.

## Linear Equation Solver
Equation of $ax + b = cx +d$ would be easy to solve by rearranging the function into $(a - c)x = d - b$, solving it with this equation: $$x = {d - b \over a - c}$$ Where $a \ne c$

``` golang
func linearEqn() {
  // Declare coefficients
	var a, b, c, d float64

	fmt.Println("Linear Equation Solver")
	fmt.Println("Eqation in the form of ax + b = cx + d ")

  // Scan and check for null or empty values
	_, err := fmt.Scan(&a, &b, &c, &d)
	if err != nil {
		panic(err)
	}

	if a == c && b == d {
		fmt.Println("There are infinite solutions to this equation")
	} else if a == c {
		fmt.Println("This equations are parallel to each other, hence no root")
	} else {
		x := (d - b) / (a - c)
		y := a*x + b
		fmt.Println("Equation: (" + FloatToString(a) + ")x + (" + FloatToString(b) + ") = (" + FloatToString(c) + ")x + (" + FloatToString(d) + ")")
		fmt.Println("The value of x:", x)
		fmt.Printf("OR the line intersects at (%g,%g)\n", x, y)

	}
}
```

## Quadratic Equation Solver
A Quadratic equation in the form of $ax^2 + bx + c = 0$, can be solved with the following equation: $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}$$
The program will first solve for the discriminant $b^2 - 4ac$ to determine the number of roots, and thereafter solve for the roots of the equation where the $discriminant \ge 0$

```golang
func quadraticEqn() {
	var a, b, c float64

	fmt.Println("Quadric Equation Solver")
	fmt.Println("Equation in the form of ax^2+bx+c = 0")
	fmt.Println("Where a > 0")
	fmt.Println()
	fmt.Println("Enter a, b, c, each in a new line:")

	// Scan and check for null or empty variables
	_, err := fmt.Scan(&a, &b, &c)
	if err != nil {
		panic(err)
	}

  // Panic if coefficient of x^2 <= 0
	if a <= 0.0 {
		panic("Coefficient of a cannot be <= 0")
	} else {

		eqn := "(" + FloatToString(a) + ")x^2 +(" + FloatToString(b) + ")x +(" + FloatToString(c) + ")"
		fmt.Println("Equation:", eqn)
		fmt.Println("a:", a)
		fmt.Println("b:", b)
		fmt.Println("c:", c)

    // Solve of discriminant
		discriminant := b*b - 4*a*c
		fmt.Println("Discriminant:", discriminant)

		if discriminant < 0 {
			// No Real Roots
			fmt.Println("Equation has no real roots")

		} else if discriminant == 0 {
			// 1 real root
			alpha := (-b + math.Sqrt(discriminant)) / (2.0 * a)
			fmt.Printf("x = %g\n", alpha)

		} else {
			//2 real roots
			alpha := (-b + math.Sqrt(discriminant)) / (2.0 * a)
			beta := (-b - math.Sqrt(discriminant)) / (2.0 * a)
			fmt.Printf("x = %g or x = %g\n", alpha, beta)

		}

	}

}
```

## Main method
This will be the Terminal UI(TUI) to get users to choose the type of equation
``` golang
func main() {
	fmt.Println("Equation Solver by Devoalda")
	fmt.Println("Enter type of equation:")
	fmt.Println("1. Linear Equation (ax + b = cx + d)")
	fmt.Println("2. Quadratic Equation (ax^2 + bx + c = 0)")

	//Single Variable scan
	var choice int
	_, err := fmt.Scanf("%d", &choice)
	if err != nil {
		panic(err)
	}

	//Switch case
	switch choice {
	case 1:
		linearEqn()
	case 2:
		quadraticEqn()
	default:
		fmt.Println("Unrecognised choice, quitting program now!")
		os.Exit(3)
	}
}
```

# Summary
The Program can be executed with `go run main.go`. All coefficients can be integers or floats.

## Full Code
``` golang
package main

import (
	"fmt"
	"math"
	"os"
	"strconv"
)

func main() {
	fmt.Println("Equation Solver by Devoalda")
	fmt.Println("Enter type of equation:")
	fmt.Println("1. Linear Equation (ax + b = cx + d)")
	fmt.Println("2. Quadratic Equation (ax^2 + bx + c = 0)")

	//Single Variable scan
	var choice int
	_, err := fmt.Scanf("%d", &choice)
	if err != nil {
		panic(err)
	}

	//Switch case
	switch choice {
	case 1:
		linearEqn()
	case 2:
		quadraticEqn()
	default:
		fmt.Println("Unrecognised choice, quitting program now!")
		os.Exit(3)
	}
}

func linearEqn() {
	var a, b, c, d float64

	fmt.Println("Linear Equation Solver")
	fmt.Println("Eqation in the form of ax + b = cx + d ")

	_, err := fmt.Scan(&a, &b, &c, &d)
	if err != nil {
		panic(err)
	}

	if a == c && b == d {
		fmt.Println("There are infinite solutions to this equation")
	} else if a == c {
		fmt.Println("This equations are parallel to each other, hence no root")
	} else {
		x := (d - b) / (a - c)
		y := a*x + b
		fmt.Println("Equation: (" + FloatToString(a) + ")x + (" + FloatToString(b) + ") = (" + FloatToString(c) + ")x + (" + FloatToString(d) + ")")
		fmt.Println("The value of x:", x)
		fmt.Printf("OR the line intersects at (%g,%g)\n", x, y)

	}
}

func quadraticEqn() {
	var a, b, c float64

	fmt.Println("Quadric Equation Solver")
	fmt.Println("Equation in the form of ax^2+bx+c = 0")
	fmt.Println("Where a > 0")
	fmt.Println()
	fmt.Println("Enter a, b, c, each in a new line:")

	_, err := fmt.Scan(&a, &b, &c)
	if err != nil {
		panic(err)
	}

	if a <= 0.0 {
		panic("Coefficient of a cannot be <= 0")
	} else {

		eqn := "(" + FloatToString(a) + ")x^2 +(" + FloatToString(b) + ")x +(" + FloatToString(c) + ")"
		fmt.Println("Equation:", eqn)
		fmt.Println("a:", a)
		fmt.Println("b:", b)
		fmt.Println("c:", c)

		discriminant := b*b - 4*a*c
		fmt.Println("Discriminant:", discriminant)

		if discriminant < 0 {
			// No Real Roots
			fmt.Println("Equation has no real roots")

		} else if discriminant == 0 {
			// 1 real root
			alpha := (-b + math.Sqrt(discriminant)) / (2.0 * a)
			fmt.Printf("x = %g\n", alpha)

		} else {
			//2 real roots
			alpha := (-b + math.Sqrt(discriminant)) / (2.0 * a)
			beta := (-b - math.Sqrt(discriminant)) / (2.0 * a)
			fmt.Printf("x = %g or x = %g\n", alpha, beta)

		}

	}

}

func FloatToString(input_num float64) string {
	// to convert a float number to a string
	return strconv.FormatFloat(input_num, 'f', 3, 64)
}
```
## Building the program
Build the go project at the **project root** with the command `go build`
If `$GOPATH` is in your `$PATH`, you can run the program with the program name `eqn`
The compiled binary is located in `$GOROOT/bin/`, where you can run the program with `./eqn`
{{< expand "Credits" >}}
<a target="_blank" href="https://icons8.com/icons/set/formula-fx">Formula FX icon</a> icon by <a target="_blank" href="https://icons8.com">Icons8</a>
{{< /expand >}}