Compare the pair
Boolean values commonly arise when you need to compare strings, numbers, or something else. Is the number 1 less than 2? Of course the expression \(1 < 2\) is true. Here are some more mathematics facts:
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/**
* Comparing numbers.
*
* @param {NS} ns The Netscript API.
*/
export async function main(ns) {
const a = 1;
const b = 2;
ns.tprintf(`${a} < ${b}? ${a < b}`);
ns.tprintf(`${a} > ${b}? ${a > b}`);
ns.tprintf(`${a} <= ${b}? ${a <= b}`);
ns.tprintf(`${a} >= ${b}? ${a >= b}`);
ns.tprintf(`${a} = ${b}? ${a === b}`);
ns.tprintf(`${a} != ${b}? ${a !== b}`);
}
Carefully examine the above program. Why the triple equal signs ===? The operator === is used in JavaScript to mean strict equality. JavaScript also uses the operator == (double equal signs) to compare numbers, but the comparison is looser and not as strict as ===. For example, JavaScript allows you to compare a number with a string as in the expression 2 == "2", which is valid JavaScript code and returns true. Strictly speaking, the number 2 is different from its string representation "2". The expression 2 === "2" returns false, which is what you would expect because a number is not the same as a string. Avoid using == as much as possible. Stick to the strict equality operator ===. Similarly, JavaScript uses the operator !== to decide whether two numbers are different. There is the looser version !=, but you should use !== as much as possible.
Does JavaScript allow you to use the above operators to compare strings? Of course. Use === to determine whether two strings are the same. Similarly, use !== to see whether two strings are different.
Exercises
Exercise 1. Read more about loose and strict equality here.
Exercise 2. Explain why the program below gives you different answers.
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/**
* Same or different?
*
* @param {NS} ns The Netscript API.
*/
export async function main(ns) {
const n = 2;
const a = n != "2";
const b = n !== "2";
ns.tprintf(`${n} != "2"? ${a}`);
ns.tprintf(`${n} !== "2"? ${b}`);
}
Exercise 3. Why are the strings "Meow" and "meow" different? Write a program to convert either or both strings so the resulting strings compare equal according to ===.
Exercise 4. The number 123 is not strictly the same as the string "123". However, you can use the JavaScript function parseInt(string, radix) to convert "123" to an integer. Replace string with "123" and replace radix with the base of the number system you want to use. For now, you want to interpret "123" as an integer according to the decimal number system, hence replace radix with 10 to mean the decimal number system. The code parseInt("123", 10) will convert "123" to an integer. Furthermore, if a string such as "123.45" can be interpreted as a floating point number, you can use the function parseFloat(string) to convert the string to a floating point number. Using parseFloat() is simpler than using parseInt() because parseFloat() always uses the decimal number system. Modify the program parse-num.js below so the relevant values compare equal according to ===.
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/**
* Same or different?
*
* @param {NS} ns The Netscript API.
*/
export async function main(ns) {
const a = 42;
const b = 42.3;
const as = "42";
const bs = "42.3";
ns.tprintf(`${a} = ${as}? ${a === as}`);
ns.tprintf(`${b} = ${bs}? ${b === bs}`);
}
Exercise 5. The function Number() provides a convenient way to convert a number from string representation to the number data type. Repeat this exercise, but using Number() only.
Exercise 6. Instead of converting "123" to a number so it would compare equal to 123, you can use the code String(n) to convert the number 123 to a string and then perform the comparison. For example, 123 would be converted to a string like so: String(123). Use String() to modify the program parse-num.js above so the relevant values would compare equal according to ===.
Exercise 7. The inequality operators <, >, <=, and >= also work with characters of the English alphabet. Just like the integers have an ordering to tell you that \(1 < 2\) holds true, characters of the English alphabet have an ordering as well, i.e. alphabetic or lexicographic ordering. The letter “a” always comes before “b” and JavaScript can confirm this dictionary ordering if you run the code "a" < "b". Here, the operator < means “precede”. The expression "a" < "b" can be read as: Does the letter “a” come before “b”? Note that in JavaScript, an uppercase letter always precedes any lowercase letter. Modify the program below so the result of the operator < is true. Why does the expression "aardvark" < "Aardvark" return false?
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/**
* A small dictionary.
*
* @param {NS} ns The Netscript API.
*/
export async function main(ns) {
const a = "aardvark";
const b = "armadillo";
const c = "aardwolf";
const d = "Aardvark";
ns.tprintf(`${b} < ${a}? ${b < a}`);
ns.tprintf(`${c} < ${a}? ${c < a}`);
ns.tprintf(`${b} < ${c}? ${b < c}`);
ns.tprintf(`${a} < ${d}? ${a < d}`);
}
Exercise 8. Two strings might have the same length, but that does not mean they are the same string. Each character must occur at the same position in both strings. Two strings can be similar if they have the same length and characters in corresponding positions might differ by lowercase or uppercase. Write a program to help you determine which of the following strings are strictly the same and which are similar: "n00dles", "noodles", "N00dles".
Exercise 9. A quiz has 3 statements, each of which evaluates to a boolean value. The statements are shown in the program below. Modify the program to output the number of correct statements, using only boolean arithmetics. Insert your code at the location shown in the program.
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/**
* How many correct solutions.
*
* @param {NS} ns The Netscript API.
*/
export async function main(ns) {
const resultA = 2 < 3;
const resultB = 37 === "37";
const resultC = 2 === 2.0;
// Insert code here.
}