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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

            
              <div id="app"></div>

            
          
!

CSS

            
              button {
  width:40px;
  height:40px;
  padding-left: 0px !important;
  padding-right: 0px !important;
  text-align: center;
  margin: 2px;
}
button.zero {
  width:84px;  
}
html {
  box-sizing: border-box;
}

.row {
  padding-bottom: 5px;
}

.display {
  width: 184px;
  height: 50px;
  padding: 7px;
  margin-bottom: 6px;
  font-size: 34px;
  color: black;
  margin: 0 auto;
}

input { 
  text-align: right; 
}

.row {
  text-align: center;
}
            
          
!

JS

            
              //import React from 'react';
//import ReactDOM from 'react-dom';
const DOT_CHAR = '.';

const OP_PERC = '%';
const OP_DIV = '/';
const OP_MUL = '*';
const OP_MINUS = '-';
const OP_PLUS = '+';
const OP_EQUAL = '=';

const INITIAL_STATE = { 
  displayValue: "0",
  firstOperand: null,
  operator: null,
  waitOperand: false,
  displayOperations: "Start your computation"
};

class DigitKey extends React.Component {
  render() {
    const {className, label} = this.props;
    return (
      <button 
        onClick={this.props.onClick}
        type="button" 
        className={`btn btn-default ${className}`}>{label}</button>
    );
  }
}

class Calculator extends React.Component {
  constructor(props) {
    super(props);
    this.state = INITIAL_STATE;
  }
  
  inputDigit(digit) {
    const  { displayValue, waitOperand } = this.state;    
    const nextDisplayValue = (waitOperand || displayValue === "0") ? digit : (displayValue + digit);
    this.setState({ 
      displayValue: nextDisplayValue,
      waitOperand: false
    });
  }

  inputDot() {
    const  { displayValue, waitOperand } = this.state;    
    if (displayValue.indexOf(DOT_CHAR) === -1) {
      const nextDisplayValue = waitOperand ? "0" + DOT_CHAR : (displayValue + DOT_CHAR);
      this.setState({ 
        displayValue: nextDisplayValue,
        waitOperand: false
      });      
    }
  }
  
  clearDisplay() {
    this.setState(INITIAL_STATE);      
  }

  toggleSign() {
    const  { displayValue } = this.state;    
    
    let nextDisplayValue = displayValue;
    
    if (displayValue.charAt(0) === '-') {      
      nextDisplayValue = displayValue.substr(1);
    } else if (displayValue !== '0') {
      nextDisplayValue = '-' + displayValue;
    }
    
    this.setState({ 
      displayValue: nextDisplayValue
    });      
  }
  
  inputOperator(nextOperator) {
    const {
      displayValue,
      firstOperand,
      secondOperand,
      operator,
      waitOperand
    } = this.state;

    const execOperator = {
      [OP_DIV]: (firstOperand, secondOperand) => firstOperand / secondOperand,
      [OP_MUL]: (firstOperand, secondOperand) => firstOperand * secondOperand,
      [OP_MINUS]: (firstOperand, secondOperand) => firstOperand - secondOperand,
      [OP_PLUS]: (firstOperand, secondOperand) => firstOperand + secondOperand,
      [OP_PERC]: (firstOperand, secondOperand) => firstOperand * secondOperand / 100,
      [OP_EQUAL]: (firstOperand, secondOperand) => secondOperand,
    };
    
    let nextDisplayValue = displayValue;
    let currentOperand = parseFloat(displayValue);
    
    if (!operator) {
      // no previous operator was set
      // same display value which will be the first operand

    } else {
           
      // there was already an operator set
      // the current display value is the second operand
      // execute the operator, the result is the next display value
      // and it is also the future first operand of the next operator
      
      if (nextOperator === OP_PERC) {
        const percentage = execOperator[nextOperator](firstOperand, currentOperand);
        // it will be the second operand
        nextDisplayValue = String(percentage);
        // reset operation and first operand
        nextOperator = operator;
        currentOperand = firstOperand;
      } else {
        currentOperand = execOperator[operator](firstOperand, currentOperand);
        nextDisplayValue = String(currentOperand);
      }
    }

    this.setState({ 
      displayValue: nextDisplayValue,
      firstOperand: currentOperand,
      operator: nextOperator,
      waitOperand: true
    });
    
  }
  
  render() {
    const  { displayValue } = this.state;
    return (
<div className="container">

  <div className="row">
    <div className="col-sm-4">
    </div>
    <div className="col-sm-4">
      <div className="row">
        <div className="title"><h4>React Calculator</h4></div>
      </div>
      <div className="row">
        <div className="display">
        <input 
          type="text" 
          className="form-control" 
          disabled 
          placeholder={displayValue} 
          title={displayValue}
        />
        </div>
      </div>
      <div className="row">
        <DigitKey onClick={() => this.clearDisplay()} label="AC" className="btn-danger" />        
        <DigitKey onClick={() => this.toggleSign()} label="±" />
        <DigitKey onClick={() => this.inputOperator(OP_PERC)} label="%" />
        <DigitKey onClick={() => this.inputOperator(OP_DIV)} label="÷" />
      </div>
      <div className="row">
        <DigitKey onClick={() => this.inputDigit("7")} label="7" />
        <DigitKey onClick={() => this.inputDigit("8")} label="8" />
        <DigitKey onClick={() => this.inputDigit("9")} label="9" />
        <DigitKey onClick={() => this.inputOperator(OP_MUL)} label="×" />
      </div>
      <div className="row">
        <DigitKey onClick={() => this.inputDigit("4")} label="4" />
        <DigitKey onClick={() => this.inputDigit("5")} label="5" />
        <DigitKey onClick={() => this.inputDigit("6")} label="6" />
        <DigitKey onClick={() => this.inputOperator(OP_MINUS)} label="-" />
      </div>
      <div className="row">
        <DigitKey onClick={() => this.inputDigit("1")} label="1" />
        <DigitKey onClick={() => this.inputDigit("2")} label="2" />
        <DigitKey onClick={() => this.inputDigit("3")} label="3" />
        <DigitKey onClick={() => this.inputOperator(OP_PLUS)} className="btn-warning" label="+" />
      </div>
      <div className="row">
        <DigitKey onClick={() => this.inputDigit("0")} className="zero" label="0" />
        <DigitKey onClick={() => this.inputDot()} label="." />
        <DigitKey onClick={() => this.inputOperator(OP_EQUAL)} label="=" />
      </div>
    </div>
    <div className="col-sm-4">
    </div>
  </div>
  
</div>

    )
  }
}

ReactDOM.render(
    <Calculator/>, 
    document.getElementById('app')
);

            
          
!
999px

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