Add otc.sol

src/pages/defi/otc/index.md

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+---
+title: OTC Exchange Examples
+version: 0.8.13
+description: OTC Exchange examples
+---
+
+### Single Desk OTC Exchange Examples
+
+```solidity
+{{{single_desk_otc}}}
+```
+
+### Multi-Desk OTC Exchange Examples
+
+```solidity
+{{{otc}}}
+```
+### Links
+

src/pages/defi/otc/otc.sol

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+// SPDX-License-Identifier: GPL-3.0
+pragma solidity >=0.7.0 <0.9.0;
+
+contract OTC {
+    uint256 public counter;
+
+    struct Order {
+        address owner;
+        address bid_token;
+        address ask_token;
+        uint bid_amount;
+        uint ask_amount;
+    }
+
+    Order[] public orders;
+
+    function give(address bid_token, address ask_token, uint bid_amount, uint ask_amount) public {        
+        IERC20(bid_token).transferFrom(msg.sender, address(this), bid_amount);        
+        orders.push(Order({
+            owner: msg.sender,
+            bid_token: bid_token,
+            ask_token: ask_token,
+            bid_amount: bid_amount,
+            ask_amount: ask_amount
+        }));
+    }
+
+    function take(uint id) public {
+        IERC20(orders[id].ask_token).transferFrom(msg.sender, orders[id].owner, orders[id].ask_amount);
+        IERC20(orders[id].bid_token).transfer(msg.sender, orders[id].bid_amount);
+        orders[id].bid_amount = 0;
+        orders[id].ask_amount = 0;        
+    }
+
+    function withdraw(uint id) public {
+        require(msg.sender == orders[id].owner, "Owner mismatch");
+        IERC20(orders[id].bid_token).transfer(msg.sender, orders[id].bid_amount);
+        orders[id].bid_amount = 0;
+        orders[id].ask_amount = 0;
+    }
+}
+
+interface IERC20 {
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address who) external view returns (uint256);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function transfer(address to, uint256 value) external returns (bool);
+
+    function approve(address spender, uint256 value) external returns (bool);
+
+    function transferFrom(address from, address to, uint256 value) external returns (bool);
+
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+}

src/pages/defi/otc/single_desk_otc.sol

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+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity >=0.7.0 <0.9.0;
+
+contract TokenExchange {
+    address fromAddress;
+    address fromToken;
+    uint256 fromAmount;
+    address toToken;
+    uint256 toAmount;
+
+    function CreateExchange(address _fromToken, address _toToken, uint256 _fromAmount, uint256 _toAmount) public {
+        IERC20(_fromToken).transferFrom(msg.sender, address(this), _fromAmount);
+        fromAddress = msg.sender;
+        fromToken = _fromToken;
+        fromAmount = _fromAmount;
+        toToken = _toToken;
+        toAmount = _toAmount;
+    }
+
+    function DoChange() public {
+        IERC20(toToken).transferFrom(msg.sender, address(this), toAmount);
+        IERC20(fromToken).transfer(msg.sender, fromAmount);
+        IERC20(toToken).transfer(fromAddress, toAmount);
+    }
+}
+
+interface IERC20 {
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address who) external view returns (uint256);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function transfer(address to, uint256 value) external returns (bool);
+
+    function approve(address spender, uint256 value) external returns (bool);
+
+    function transferFrom(address from, address to, uint256 value) external returns (bool);
+
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+}