---
# System prepended metadata

title: from C to JavaScript

---

# from C to JavaScript

## 運算子

### C
```
#include<stdio.h>
int main(void){
  int x = 4;
  int y = 3;
  
  int a = x + y;
  int b = x - y;
  int c = x * y;
  int d = x / y;
  int e = x % y;
  
  printf("%d\n",a);
  
  printf("%d\n",b);
  
  printf("%d\n",c);
  
  printf("%d\n",d);
  
  printf("%d\n",e);
}

```

C語言需要寫#include<stdio.h>
javascript不用寫

int・・・變數的宣告的時候使用.只有輸入的數字是整數的時候可以用.
（int x = ４、int y = 3　等等）

\n・・・新增一行的意思

printf・・・顯示在螢幕上()內的文字的時候使用.

+・・・加法　　　　-・・・減法　　　　*・・・乘法
/・・・除法 　　　　%・・・模數除法
javascript 也一樣的方法


### javascript
```
var x = 4;
var y = 3;

var a = x + y;
var b = x - y;
var c = x * y;
var d = x / y;
var e = x % y;

console.log(a);
console.log(b);
console.log(c);
console.log(d);
console.log(e);
```

var・・・變數的宣告的時候使用.輸入的是都可以.
（var a = x + y、var x = 4、var z = "Hello,World!"　等等）

console.log()・・・表示()內的文字,變數的值

後面需要「;」、C語言也需要


# Quiz 30題
### (1)Create a variable called carName, assign the value Volvo to it.
```
var carName = "Volvo";
```
### (2)Create a variable called x, assign the value 50 to it.
```
var x = 50;
```

### (3)Display the sum of 5 + 10, using two variables: x and y.
```
var x = 5;
var y = 10;
document.getElementById("demo").innerHTML = x + y;
```

### (4)Create a variable called z, assign x + y to it, and display the result in an alert box.
```
var x = 5;
var y = 10;
var z = x + y;
alert(z);
```

### (5)On one single line, declare three variables with the following names and values: firstName = "John" lastName = "Doe" age = 35
```
var firstName = "John", lastName = "Doe", age = 35;
```

### (6)Multiply 10 with 5, and alert the result:
```
alert(10 * 5);
```

### (7)Divide 10 by 2, and alert the result:
```
alert(10 / 2);
```

### (8)Alert the remainder when 15 is divided by 9.
```
alert(15 % 9);
```

### (9)Use the correct assignment operator that will result in x being 15 (same as x = x + y).
```
x = 10;
y = 5;
x + = y;
```

### (10)Use the correct assignment operator that will result in x being 50 (same as x = x * y).
```
x = 10;
y = 5;
x * = y;
```
### (11)Use comments to describe the correct data type of the following variables:
```
let length = 16;           //number
let lastName = "Johnson";  //string
const x = {
  firstName: "John",
  lastName: "Doe"
};                         //object
```

### (12)Execute the function named myFunction.
```
function myFunction() {
  alert("Hello world!");
}
myFunction();
```

### (13)Create a function called "myFunction"
```
function myFunction(){
  alert("Hello,World!");
}
```

### (14)Make the function return "Hello"
```
function myFunction() {
  return "Hello";
}
```

### (15)Make the function display "Hello" in the inner HTML of an element with the ID "demo".
```
function myFunction() {
  document.getElementById("demo").innerHTML = "Hello";
}
```

### (16)Alert "John" by extracting information from the person object.
```
const person = {
  firstName: "John",
  lastName: "Doe"
};

alert(person.firstName);
```

### (17)Add the following property and value to the person object: country: Norway.
```
const person = {
  firstName: "John",
  lastName: "doe",
  country: "Norway"
};
```

### (18)Create an object called person with name = John, age = 50.Then, access the object to alert("John is 50").
```
const person = {
  name: "John", age:50
};
alert(person.name + "is" + person.age);
```

### (19)The<button> element should do something when someone clicks on it. Try to fix it!
```
<button onclick = "alert('Hello')">Click me.</button>
```

### (20)When the button is clicked, the function "myFunction" should be executed.
```
<button onclick = "myFunction()">Click me.</button>
```

### (21)The < div > element should turn red when someone moves the mouse over it.
```
<div onmouseover = "this.style.backgroundColor = 'red'">myDIV.</div>
```

### (22)Use the length property to alert the length of txt.
```
let txt = "Hello World!";
let x = txt.length;
alert(x);
```

### (23)Use escape characters to alert We are "Vikings".
```
let txt = "We are \"Vikings\"";
alert(txt);
```

### (24)Concatenate the two strings to alert "Hello World!".
```
let str1 = "Hello ";
let str2 = "World!";
alert(str1 + str2);
```

### (25)Convert the text into an UPPERCASE text:
```
let txt = "Hello World!";
txt = txt.toUpperCase();
```

### (26)Use the slice method to return the word "bananas".
```
let txt = "I can eat bananas all day";
let x = txt.slice(10,17);
```

### (27)Use the correct String method to replace the word "Hello" with the word "Welcome".
```
let txt = "Hello World";
txt = txt.replace("Hello", "Welcome");
```

### (28)Convert the value of txt to upper case.
```
let txt = "Hello World";
txt = txt.toUpperCase();
```

### (29)Convert the value of txt to lower case.
```
let txt = "Hello World";
txt = txt.toLowerCase();
```

### (30)Get the value "Volvo" from the cars array.
```
const cars = ["Saab", "Volvo", "BMW"];
let x = cars[1];
```
