# Writing a smart contract in Golang (Go)

This example will show how to write a smart contract in Golang.

## Sample contract functionality <a href="#sample-contract-functionality" id="sample-contract-functionality"></a>

The sample contract serves as a demonstration of general QVM logic.

It is capable of:

* registering users into the database
* storing the last registered user's name in the database
* echoing the previous user's name to STDOUT
* incrementing the total registered user count
* storing above counter in the database

## Sample code <a href="#sample-code" id="sample-code"></a>

```go
package main

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

func main() {

    // THIS SAMPLE ONLY SUPPORTS THE "register" FUNCTION
    if len(os.Args) == 3 && os.Args[1] == "register" {

        // GET THE CURRENT USER'S NAME
        previousName := os.Getenv("DB_USER_CURRENT")

        // OR DEFAULT TO "unknown" IF THIS IS THE FIRST CALL
        if len(previousName) == 0 {
            previousName = "unknown"
        }

        // GET THE TOTAL USER COUNT
        totalUserCount, _ := strconv.Atoi(os.Getenv("DB_TOTALUSERS"))

        // WRITE PREVIOUS USER NAME TO STDOUT
        os.Stdout.WriteString(fmt.Sprintf("OUT=prevname: %s\n", previousName))

        // UPDATE CURRENT USER NAME BY WRITING IT TO DB
        os.Stdout.WriteString(fmt.Sprintf("DBW=USER_CURRENT=%s\n", os.Args[2]))

        // STORE USER NAME UNDER A STORAGE SLOT FOR PERSISTENCE (CURRENT GETS OVERWRITTEN ON EACH CALL)
        os.Stdout.WriteString(fmt.Sprintf("DBW=USER_%d=%s\n", totalUserCount, os.Args[2]))

        // INCREMENT THE TOTAL USER COUNT
        os.Stdout.WriteString(fmt.Sprintf("DBW=TOTALUSERS=%d\n", totalUserCount+1))
        os.Exit(0)
    }
    if len(os.Args) >= 2 {
        os.Stderr.WriteString(fmt.Sprintf("Wrong CMD:%s\n", os.Args[1]))
        os.Exit(1)
    }
    os.Stderr.WriteString("Wrong args!\n")
    os.Exit(1)
}
```

## Save the contract <a href="#save-the-contract" id="save-the-contract"></a>

Open a text editor and save above sample contract as `main.go` file.