freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/understanding-uninitialized-variables.english.md

id	title	challengeType	videoUrl
56533eb9ac21ba0edf2244aa	Understanding Uninitialized Variables	1	https://scrimba.com/c/cBa2JAL

Description

When JavaScript variables are declared, they have an initial value of undefined. If you do a mathematical operation on an undefined variable your result will be NaN which means "Not a Number". If you concatenate a string with an undefined variable, you will get a literal string of "undefined".

Instructions

Initialize the three variables a, b, and c with 5, 10, and "I am a" respectively so that they will not be undefined.

Tests

tests:
  - text: <code>a</code> should be defined and evaluated to have the value of <code>6</code>
    testString: assert(typeof a === 'number' && a === 6, '<code>a</code> should be defined and evaluated to have the value of <code>6</code>');
  - text: <code>b</code> should be defined and evaluated to have the value of <code>15</code>
    testString: assert(typeof b === 'number' && b === 15, '<code>b</code> should be defined and evaluated to have the value of <code>15</code>');
  - text: <code>c</code> should not contain <code>undefined</code> and should have a value of "I am a String!"
    testString: assert(!/undefined/.test(c) && c === "I am a String!", '<code>c</code> should not contain <code>undefined</code> and should have a value of "I am a String!"');
  - text: Do not change code below the line
    testString: assert(/a = a \+ 1;/.test(code) && /b = b \+ 5;/.test(code) && /c = c \+ " String!";/.test(code), 'Do not change code below the line');

Challenge Seed

// Initialize these three variables
var a;
var b;
var c;

// Do not change code below this line

a = a + 1;
b = b + 5;
c = c + " String!";

After Test

(function(a,b,c){ return "a = " + a + ", b = " + b + ", c = '" + c + "'"; })(a,b,c);

Solution

var a = 5;
var b = 10;
var c = "I am a";
a = a + 1;
b = b + 5;
c = c + " String!";