# Technical ## **How can I develop and deploy a DApp (Decentralized Application) on Qtum?** DApps use a smart contract working with external servers and user interfaces. Qtum smart contracts are written in the Solidity programming language and compiled to EVM bytecode. That code is published to the blockchain using a contract create transaction which costs approximately 1.1 QTUM in gas and transaction fees. The smart contract operation can be linked with a server and user interfaces (for example on web or mobile apps) to complete the Decentralized Application.\ Publishing a smart contract on Qtum is permissionless (anyone can do it). Qtum smart contract and DApp development follows familiar patterns from Ethereum and web/mobile apps. To engage with Qtum’s experienced DApp team please submit the [DApp application form](https://qtum.org/en/developer/long-term/dapp).Have you had a chance to answer the previous question? ## **How do I set the confirmation number when the exchange handles user recharge?** Recommended to be set to 10 to 20. ## **How does the exchange handle the recharge of the QRC20 Token?** Please refer to [QRC20 Integration Technical Document](https://docs.qtum.site/zh/QRC20%E9%9B%86%E6%88%90%E6%96%87%E6%A1%A3.html) ## **What is the BIP44 Coin Type value of Qtum?** BIP44 Coin Type is 88. ## **What is the difference between Qtum and Bitcoin RPC interface?** In addition to adding createcontract\sendtocontract\callcontract\searchlogs\gettransactionreceipt , all the rest of the RPC interfaces are almost identical to Bitcoin. ## **How to set the gas limit and price of calling contract?** It is recommended to fix the gas price to 0.00000040. For QRC20 Token transactions, the gas limit is recommended to be set to 250000. ## **How is the remaining gas returned after the contract is called?** When the transaction is confirmed, the more paid gas will be in the second transaction of the block in the form of a coin stake transaction. ## **How to get test coins?** Please go to [Testnet Faucet](http://testnet-faucet.qtum.info/#!/) to apply. ## **Does Qtum support calling contracts with multiple signature addresses?** Multi-signature currently does not support calling contracts and sending and receiving QRC20 Tokens. It is planned that this feature will be implemented in x86 virtual machines. ## What public APIs are available for Qtum nodes, how do you use them? qtum.info API\ Documentation \ Examples**：**\ Mainnet API = /... Testnet API = ...\ Block data：\ \ Transaction data ： ![](https://3709248542-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lh9f6HdHMs3j0TOD2-u%2F-Lh9iScAkdOi9v4ux5rd%2F-Lh9mHDHDd3FvyJo_zta%2Fimage.png?alt=media\&token=e6f1d428-08c1-40c4-b7ba-76221156ba45) ## How to use mobile wallet API? Documentation \ Examples:\ Unspent transactions \ Last added contracts See also the iOS wallet code RequestManager.m and the Android code QtumRestService.java, which should give all the calls these wallets use with this mobile API. ## Do you have an Amazon AWS platform? Yes, Qtum’s development platform is available on Amazon Web Services. Users across the enterprise and elsewhere will now be able to develop and deploy their own smart contracts from this ready-to-use Amazon Machine Image (AMI) featuring Qtum core, and the Qmix Integrated Development Environment (IDE).\ Blog \ AWS AMI ## What wallets/nodes are available for smart contract transactions? 1\. The Qtum Core wallet is a full node with smart contract capability via GUI or command line. Available for multiple platforms. Works on Mainnet, Testnet & Regtest.\ Documentation \ Releases 2\. The Qtum web wallet is a light wallet that can create, send and call contracts, but currently can’t send QTUM to a contract address. Works on Mainnet and Testnet.\ Documentation \ Wallet Website 3\. The Chrome extension Qrypto is a light wallet that can make DApp interface contract calls through the Qweb3 library. Works on Mainnet, Testnet & Regtest\ Documentation \ Plugin \ Qweb3 library ## What developer blogs are available? See Qtum101 at such as:\ QTUM: Decentralized Governance Protocol Video Demo\ Atomic Cross-Chain Swaps on Qtum\ How to: Build a DApp based on Qtum and IPFS\ QTUM Tutorial: Building a Contract Calling Raw Transaction\ Developers Guide to the Qtum GitHub See Unita blogs at such as:\ QtumX Reaches 10,000 TPS in Benchmark Tests\ Atomic Cross-Chain Swaps on Qtum\ DDAO: Decentralized Data Access Object\ SCAR: A New Scalable Consensus Algorithm ## How can I use the Explorers to monitor smart contract transactions? See transaction detail and the event log with qtum.info, for example \ Click on the red script to expand. ![](https://3709248542-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lh9f6HdHMs3j0TOD2-u%2F-Lh9o_4hr9qNL9fjGkE6%2F-Lh9oxHjRsARALxZNCbM%2Fimage.png?alt=media\&token=6ae21413-5d7a-4eef-8996-863688acedcd) See QRC20 balances by entering an address in the “BalanceOf” field for a contract, for example ![](https://3709248542-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lh9f6HdHMs3j0TOD2-u%2F-Lh9o_4hr9qNL9fjGkE6%2F-Lh9p5ptkvMOYHs3GKqU%2Fimage.png?alt=media\&token=539481df-b54f-4f47-afcf-0ecc639d5ece) See the storage table, for example ![](https://3709248542-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lh9f6HdHMs3j0TOD2-u%2F-Lh9o_4hr9qNL9fjGkE6%2F-Lh9pAq_cdzoxigwm2Q_%2Fimage.png?alt=media\&token=5c98e7ed-7343-487e-a351-574f40350502) ## How can I setup Docker and run a Regtest Qtum node? IAME blog ## How do I access the Qtum Testnet? User guide \ Explorer \ Explorer 2 \ Faucet ## Is there a command line smart contract tool like solc for Qtum? Yes, see solar ## Is there a web IDE like remix for Qtum? Yes, Qmix