I have a function that gives me a random number inbetween two numbers. That function works.
I have a conditional statement below the function that's supposed to change my variable from false to true, but when I console.log the variable, it is still false. My conditional statement is true, when I console.log actualGetRandom, it comes out to either 10 or 11, but the code between the curly braces is not executed. Not sure why and need some input. Thanks.
function getRandomIntInclusive(min, max) {
min = Math.ceil(min);
max = Math.floor(max);
return Math.floor(Math.random() * (max - min + 1)) + min;
}
var isBetween10And11 = false;
var actualGetRandom = getRandomIntInclusive(10, 11);
if (actualGetRandom >= 10 && actualGetRandom <= 11) {
console.log("I'm here");
isBetween10and11 = true;
}
The if statement is exectued!
There is a typo in your code which makes it inconsistent:
var isBetween10And11 = false;
...
isBetween10and11 = true;
Definition of variable: ...And...
Use of variable ...and...
Best way to avod this: use editor with autocompletion and use it a lot.
Best way to spot it: Use a debugger
Related
I want to be able to generate a boolean condition during the runtime based on the states of some variables. My task looks simple at first. I have a large if () else if () statement what needs to determine if the number is in a certain range. It then does something depending on whether that number is inside that range.
Here's pseudocode to demonstrate what I want:
void fun(int num, int offset = 0) {
if (0...60) {
// do something
} else if (60...180) {
// do something else
} else if (180...240) {
} else if (240...360) {
}
}
The first if statement should work like this:
if (0 >= num && num <= 20) {
// do something
}
The caveat here is that in addition to int num, there is another parameter passed in, which I call the offset. The structure of the code here, including the do something inside the { } is the same. The only things that need to change are are ranges, based on the value of the offset. By the way, this is not a default parameter here, it is just pseudocode demonstrating what the value of int offset was passed in.
void fun(int num, int offset = 120) {
if (120...180) {
// do something
} else if (180...300) {
// do something else
} else if (300...360) {
} else if (360...120) {
}
}
That last else if () statement has been giving me some trouble.
} else if (360...120) {
}
What I'm actually trying to write here is:
} else if (num >= 360 || num <= 120) {
}
The reason for this is that my int num may have a value > 360. However, in that case for the purpose of my application it has to "wrap around" and be treated as a value 0...120.
This is for a mathematical application here. Whenever you have int num > 360, you go around the full circle and you end back at 0 where you started. So that is the effect which I want to achieve.
I don't want to write extra functions. I want my code to be generic because many different values for int num and int offset may be passed into my function. I want to generate the necessary conditions during the runtime based on the value of int offset.
The main problem here is that in the first situations, when int offset = 0 my condition is
} else if (240 >= num && num <= 360) {
}
However, for a different offset we wrap around and so I have to change the format of the entire condition! For example, when int offset = 120, as shown above:
} else if (num >= 360 || num <= 120) {
}
The problem is that in the first situation I had the && in the last else if (), but now I have the || to convey the same meaning. What I'm looking for is a way to be able to manipulate the operators inside the conditional statements as mere chars in a string, then "paste" the completed condition into the if () statements during the runtime!
What's even worse is that this "wrapping around" can occur inside any one of the if () statements, not just the last one. It is based on the value of the offset.
I can't use preprocessor tricks, because I want this to work during the runtime. Maybe it is possible to use function pointers or something for this, but I don't know how to do that. Please note that the ... above is not real C++ code, it is pseudocode! I'm aware that there is a "range-based" switch statement in C++, but I can't use that because of the "wrapping around" property mentioned above.
I don't quite understand the meaning of else if statements.
why not just to continue with the if statements in case one is false?
it works the same.
example with if only that will work the same with else if:
function testSize(num) {
if (num < 5){
return "Tiny";
}
if (num < 10){
return "small";
}
return "Change Me";
}
testSize(7);
In your actual code you specify a return statement in the code associated to the if statement.
Suppose you don't specify a return statement or suppose today you specify a return statement but tomorrow you remove it to do a common return at the end of the method.
This code will test each condition even if the first one is true :
if (num < 5){
// do something
}
if (num < 10){
// do something
}
This code will not test the next condition if the first one is true :
if (num < 5){
// do something
}
else if (num < 10){
// do something
}
These two ways of doing have two distinct meanings.
When you have a series of if statements, you expect that more than one condition may be true.
When you have a series of if-else-if statements, you expect to have not more than one condition true.
Using the first form (a series of if) while functionally you expect to have not more than one condition true is misleading.
Besides, if the code is modified and you add a condition that is both true for two if statements while you don't want have this case, it would create an issue.
Your code is only showing your belief. What would happen in the example below?
function testSize(num) {
if (num < 5){
x = 1;
}
if (num < 10){
x = 2;
}
result = complex calculations;
}
function testSize2(num) {
if (num < 5){
x = 1;
} else if (num < 10){
x = 2;
}
return x * 2;
}
testSize(4); // result is 4
testSize2(4); // result is 2
x may also be involved in more calculations
if(condition) {...}
if(condition) {...}
if(condition) {...}
In above code, even if the first or second condition is true, third condition have to be checked.
if(condition) {}
else if(condition){}
else if(condition){}
Here if first condition is true, next two will not be checked. So, it saves time and is more readable logically.
A one way if statement takes an action if the specified condition is true.If the condition is false, nothing is done. But what if you want to take alternative actions when the conditions is false ? You can use a two-way if-else statement. The action that a two-way if-else statements specifies differ based on whether the condition is true or false.
Well, there is a bit different from this two statement.Consider the follow samples
if(a > 0) {
...
}
if( a == 0) {
...
}
if(a < 0) {
...
}
and
if(a > 0) {
...
}
else if( a == 0) {
...
}
else if(a < 0) {
...
}
when a is zero the last else if statement will not be execute while if need to compare third time.If a equals to 10, else if could be execute once while if is third.From this else if statement could be execute less and let your program a bit fast.
else if should be used when there are multiple conditions and you want only one of them to be executed, for instance:
if(num<3){ console.log('less than 3') }
else if(num<2){ console.log('less than 2')
If you use multiple if statements instead of using else if, it will be true for both the conditions if num = 1, and therefore it will print both the statements.
Multiple if statements are used when you want to run the code inside all those if statements whose conditions are true.
In your case it doesn't make a difference because the function will stop and return at the very first return statement it encounters. But let's say, the blocks' orders are interchanged, then your function will never return 'tiny' even if num = (anything less than 5).
I hope that helps!
If all your if branches terminate the function (e.g., but returning a value of throwing an exception), you're right, and you really don't need an else statement (although some coding standards might recommend it).
However, if the if branches don't terminate the function, you'd have to use an else or else if clause to prevent multiple blocks from being executed. Assume, e.g., you want to log a message to the console instead of returning it:
if (num < 5) {
console.log("Tiny");
} else if (num < 10) {
console.log("small");
} else {
console.log("Change Me");
}
Can checking for a condition be turned off when that condition is met and how would this be implemented (using language of your choosing)?
Example:
Say an if-statement runs inside an update function, I would like this if-statement not to be called when the statement has run true once in the lifecycle of the program. I'm thinking this might be achieved by wrapping the statement in a function variable(javascript) then reassigning that variable to return void if/when the condition is true.
Ok let’s say you have this (C++):
void update() {
// code
if (condition) {
// code
}
// code
}
What you can do is:
void update() {
// code
static bool already_ran = false;
if (!already_ran && condition) {
alreadu_ran = true;
// code
}
// code
}
static means that the variable retains it's value over function calls and in C/C++ the logical operators (&& in this example) are short-circuited. That means that they don’t evaluate the second operand unless they need. For instance if !already_ran is false then the whole expression is false regardless of condition so condition is not evaluated.
Not 100% sure this is more efficient than using a simple condition to run the increaseValue() function but here is the code I am using and it seems to work (in as3 at least). Update is being called approx 30 times a second.
public function update(){
if(isHit){ //isHit is part of another condition used by collision
increaseValues = function() {
this.height += 1;
this.width += 1;
this.x -= 1;
this.y -= 1;
this.alpha += -0.1;
if (this.alpha == 0){
increaseValues = function(){
return;
}
}
}
}
increaseValues();
}
Here is an extremely simplified version of a section of code that I am having trouble with.
int i = 0;
int count = 0;
int time = 50;
int steps = 1000;
double Tol = 0.1;
bool crossRes = false;
bool doNext = true;
for (int i=0; i<steps; i++) {
//a lot of operations are done here, I will leave out the details, the only
//important things are that "dif" is calculated each time and doNext either
//stays true or is switched to false
if (doNext = true) {
if (dif <= Tol) count++;
if (count >= time) {
i = steps+1;
crossRes = true;
}
}
}
if (crossRes = true) {
printf("Nothing in this loop should happen if dif is always > Tol
because count should never increment in that case, right?");
}
My issue is that every time it gets done with the for loop, it executes the statements inside the "if (crossRes = true)" brackets even if count is never incremented.
You've made a common (and quite frustrating) mistake:
if (crossRes = true) {
This line assigns crossRes to true and returns true. You're looking to compare crossRes with true, which means you need another equals sign:
if (crossRes == true) {
Or more concisely:
if (crossRes) {
I stand corrected:
if (crossRes)
You wouldn't have this problem if your condition was
if (true = crossRes)
because it wouldn't compile.
`crossRes = true` always evaluates to `true` because it's an assignment, to `true`.
You want `crossRes == true`:
if (crossRes == true) {
printf("Nothing in this loop should happen if dif is always > Tol
because count should never increment in that case, right?");
}
= is assignment, == is equality comparison. You want:
if (crossRes == true) {
You make the same mistake here:
if (doNext = true) { // Bad code
The other answers here have told you the problem. Often your compiler will warn you but a way to ensure that you do not do this is to put the constant term on the left
true == crossRes
that way you get a compiler error instead of a warning and so it can't escape unnoticed since
true = crossRes
wont compile.
First, although a number of people have pointed to the problem with if (crossRes = true), for some reason they haven't (yet, anyway) pointed to the same problem with if (doNext = true).
I'll stick to pointing out that you really want if (crossRes) rather than if (crossRes == true) (or even if (true == crossRes)).
The first reason is that it avoids running into the same problem from a simple typo.
The second is that the result of the comparison is a bool -- so if if (crossRes==true) is necessary, you probably need if (((((crossRes == true) == true) == true) == true) just to be sure (maybe a few more -- you never know). This would, of course, be utterly silly -- you're starting with a bool, so you don't need a comparison to get a bool.
I'd also note for the record, that if you insist on doing a comparison at all, you should almost always use if (x != false) rather than if (x == true). Though it doesn't really apply in C++, in old C that doesn't have an actual Boolean type, any integer type can be used -- but in this case, a comparison to true can give incorrect results. At least normally, false will be 0 and true will be 1 -- but when tested, any non-zero value will count as equivalent to true. For example:
int x = 10;
if (x) // taken
if (x == true) // not taken, but should be.
If you're not starting with a Boolean value as you are here, then the if (<constant> <comparison> <variable>) makes sense and is (IMO) preferred. But when you're starting with a Boolean value anyway, just use it; don't do a comparison to produce another of the same.
I am trying to increment a lap counter in my game by one but because I have to put this code in the game loop my counter goes over every time by about 500 instead or moving up one. Here is my code. The checkpointPassed variable is only true when a checkpoint is passed through. I know this works and the checkpoint number is the current checkpoint and they start at 0.
if(checkpointNumber == 0 && checkpointPassed == true)
{
lapNumber += 1;
}
I can't post the game loop because it is quite large.
Any Help is appreciated.
EDIT
Here is some more of the code so you can see what I am trying to do.
if(distance > carRadius && markerCounter < 5000)
{
if(checkpointPassed == true)
{
markerCounter++;
}
}
if(checkpointNumber == 0 && checkpointPassed == true)
{
lapNumber += 1;
}
if(distance < carRadius)
{
markerCounter++;
cross->SetX(checkpointX);
cross->SetY(checkpointY);
cross->SetZ(checkpointZ);
checkpointNumber += 1;
checkpointPassed = true;
}
if(markerCounter > 4999)
{
checkpointPassed = false;
cross->SetPosition(0,-50,0);
markerCounter = 0;
}
Add another two variable called inCheckpoint, which stores whether the user is currently "inside" the checkpoint or not. This allows you to detect when the user enters a checkpoint and only increment the lapNumber then. The code would look as follows:
if(checkpointNumber == 0 && checkpointPassed == true)
{
if (inCheckpoint == false) /* previously not inside a checkpoint */
lapNumber += 1;
inCheckpoint = true;
}
else
{
inCheckpoint = false;
}
UPDATE: Don't rely on checkpointPassed:
if(distance < carRadius)
{
if (inCheckpoint == false) /* previously not inside a checkpoint */
lapNumber += 1;
inCheckpoint = true;
}
else
{
inCheckpoint = false;
}
You could set/pass a gueard value that indicates how many iterations in the game loop you are (or whether this is the first iteration). If it is the first iteration (within the current lap), increment the variable as you do now, otherwise don't
You will need to reset this guard value for each lap -- e.g. right after you increment lapNumber.
You might need to cancel the 'checkpointPassed` state.
if (checkpointNumber == 0 && checkpointPassed == true)
{
lapNumber += 1;
checkpointPassed = false;
}
This means that you won't be counting the lap again until the next time a checkpoint is passed, which is presumably when you need it counted.
However, if you need checkpointPassed true later in the loop, then you'll need to think whether you need yet another variable, such as lapCounted, which is set to false when checkpointPassed is set to true, and reset to true by the code above (instead of setting checkpointPassed, not as well as setting it).
If I understand correctly what you said, your 'if' statement is inside the main loop and when you pass a checkpoint, 'checkpointPassed' becomes true. For how long?
If it stays 'true' for a few iterations, then each time your game loop does an iteration,your lap counter is incremented. In this case, you should either set checkPointPassed to false at the end of the iteration, or use a different variable, that you set to true at the same time that checkPointPassed becomes true and false after incrementing.
If this does not answer your question, can you give a little more context as with only this part of the code, it is hard to figure out what you want to do.