Added a new contract Bank where people can deposit, withdraw and even take Loan.

README.md

@@ -39,4 +39,7 @@ This is a curated list of problems in Solidity for someone who is just starting
 12. [**Address Book**](./contracts/AddressBook.sol)  
     Contract to store and manage contact information.
 
+13. [**Simple Bank**](./contracts/Bank.sol)                       
+    Contract to deposit,fixedeposit,takeloan and repayloan just like a bank.
+
 ---

contracts/Bank.sol

@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+contract Bank {
+    uint public totalBankBalance; 
+    mapping(address => uint) public deposits;
+    mapping(address => Fixeddeposits) public fixeddeposits;
+    mapping(address => uint) public coinbalance;
+    mapping(address => Loantakers) public loantakers;
+
+    struct Fixeddeposits {
+        uint amount;
+        uint starttime;
+        uint endtime;
+        bool active;
+    }
+
+    struct Loantakers {
+        uint amount ;
+        uint loantime;
+        uint loanendtime;
+        bool active;
+    }
+    function deposit() public payable {
+        require(msg.value > 0, "Cannot deposit 0");
+        deposits[msg.sender] += msg.value;
+        coinbalance[msg.sender] += msg.value;
+        totalBankBalance += msg.value;        
+    }
+
+    function withdraw(address payable to, uint amount) public {
+        require(amount <= deposits[msg.sender], "Not enough balance to withdraw");
+        require(amount <= coinbalance[msg.sender], "Can't withdraw more coins than you have");
+        require(amount <= totalBankBalance, "Bank is currently out of money");
+
+        deposits[msg.sender] -= amount;
+        coinbalance[msg.sender] -= amount;
+        totalBankBalance -= amount;
+
+        to.transfer(amount);
+    }
+
+    function fixeddeposit() public payable {
+        require(msg.value > 0, "Cannot deposit 0");
+        require(fixeddeposits[msg.sender].active == false, "Already fixed deposited");
+        fixeddeposits[msg.sender] = Fixeddeposits({
+            amount: msg.value,
+            starttime: block.timestamp,
+            endtime: fixeddeposits[msg.sender].starttime + 365 days,
+            active: true
+        });
+
+        coinbalance[msg.sender] += msg.value;
+        totalBankBalance += msg.value;    
+    }
+
+    function withdrawfixeddeposit(address payable to, uint amount) public {
+        Fixeddeposits storage fd = fixeddeposits[msg.sender];
+
+        require(fd.active == true, "You have not deposited anything");
+        require(block.timestamp >= fd.starttime + 365 days, "FD is not matured yet");
+        require(amount > 0, "Cannot withdraw less than zero");
+        require(amount <= fd.amount, "Not enough in your fixed deposit");
+        require(amount <= coinbalance[msg.sender], "Not enough coins to withdraw");
+        require(amount <= totalBankBalance, "Bank is currently out of money");
+        uint interest = (fd.amount * 8) / 100;
+        fd.amount += interest;
+        fd.amount -= amount;
+        coinbalance[msg.sender] -= amount;
+        totalBankBalance -= amount;
+        if (fd.amount == 0) {
+            fixeddeposits[msg.sender] = Fixeddeposits({
+                amount: 0,
+                starttime: 0,
+                endtime: block.timestamp,
+                active: false
+            });
+        }
+
+        to.transfer(amount);
+    }
+
+function takeloan(address payable to, uint amount) public {
+    require(amount > 0, "Cannot loan less than zero");
+    require(amount <= totalBankBalance, "Bank doesn't have enough money");
+    require(!loantakers[msg.sender].active, "You already have an active loan");
+
+    loantakers[msg.sender] = Loantakers({
+        amount: amount,
+        loantime: block.timestamp,
+        loanendtime: block.timestamp + 365 days,
+        active: true
+    });
+
+    totalBankBalance -= amount;
+    to.transfer(amount);
+}
+
+function clearloan() public payable {
+    Loantakers storage lt = loantakers[msg.sender];
+    require(lt.active, "You have no active loan");
+
+    uint interest = (lt.amount * 15) / 100;
+    uint totaldue = lt.amount;
+
+    if (block.timestamp > lt.loanendtime) {
+        totaldue += interest;
+    }
+
+    require(msg.value >= totaldue, "Not enough ETH sent to repay the loan + interest");
+
+    totalBankBalance += msg.value;
+    lt.amount = 0;
+    lt.loantime = 0;
+    lt.loanendtime = 0;
+    lt.active = false;
+
+    }
+
+}