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MT4 Variable Question

  • #1
  • First Post: Edited 3:47pm Mar 11, 2021 3:33pm | Edited 3:47pm
how the MT4 distinguish between the "resultTotal" before the = as a new total that will have a new value assigned to it after operating the left side after the equal, and "resultTotal" that is on the left side after the equal as old value?


double resulttotal;
double resultaverage;
int totalbar = 10;

for(int x = 1; x <= totalbar; x++) {resulttotal = resulttotal + iClose(NULL, 0 , x); }


resultaverage = resulttotal / totalbar;

------------------------------------------------------------------------------------------------------------------------------------

what confusing me is that in the example I set resulttotal will have 2 different values because of the looping
if we said that resulttotal will start off by being equal to zero and we have a candle close that is equal to 1.9231, so it will be as follow

resulttotal = resulttotal + iClose(NULL, 0 , x);
resulttotal = 0 + 1.9231
so now I think the resulttotal will be equal to 1.9231 But on the second loop I see it as follow
1.9231 = 1.9231 + 1.9341
Which I does not understand unless I see the "resulttotal" that is before the equal as variable empty but it is not because it has a value of 1.9231 and this value has been applied by the system to the "resulttotal" that came after the = sign on the same line

So my question how the system sees the first "resulttotal" that is before the equal still as a variable that can be changed while the "resulttotal" after the equal as a variable that has a value
  • #2
  • Edited 4:29pm Mar 11, 2021 4:15pm | Edited 4:29pm
my personal preference is that variables should be initialized..

i cant say for sure if this is the cause of your problem or not, as i am not entirely understanding your issue.

Inserted Code
double resulttotal=0; //just for fun, initialize this variable..
double resultaverage=0; //same thing here.
int totalbar = 10;
for(int x = 1; x <= totalbar; x++)
{
resulttotal = resulttotal + iClose(NULL, 0 , x);
}
resultaverage = resulttotal / totalbar;


edit: i just read your post again, let me try to answer for you..

Inserted Code
 
 
resulttotal = resulttotal + iClose(NULL, 0 , x);

the above code will calculate everything that is on the right side of the equal sign first... adding the current value of resulttotal and iclose..

the outcome of that above calculation will be assigned to the variable on the left side of the equal sign.

example:

Inserted Code
int result=1;
 
result=result+2;
 
//result now now equals three;
 
result=result*2;
 
//result now equals six.
  • #3
  • Mar 11, 2021 4:41pm Mar 11, 2021 4:41pm
Quoting jmoreno
my personal preference is that variables should be initialized.. i cant say for sure if this is the cause of your problem or not, as i am not entirely understanding your issue. double resulttotal=0; //just for fun, initialize this variable.. double resultaverage=0; //same thing here. int totalbar = 10; for(int x = 1; x <= totalbar; x++) { resulttotal = resulttotal + iClose(NULL, 0 , x); } resultaverage = resulttotal / totalbar; edit: i just read your post again, let me try to answer for you.. resulttotal = resulttotal + iClose(NULL, 0 , x); the...
I understand your explanation perfectly sir,
what I am struggling with sir, is that the same "resulttotal" has been interpreted differently once as a variable and the second time as a value, which I do not understand
so if we are saying

resulttotal = resulttotal +i;
here the "resulttotal" on the left side has been interpreted as a variable while "resulttotal" on the right side has been interpreted as value although both on the same line both same-named,

and that is my question how the system could distinguish between these 2
please let me know if you want me to explain more my inquiry

thank you for your help
  • #4
  • Edited 5:31pm Mar 11, 2021 5:02pm | Edited 5:31pm
Quote
what I am struggling with sir, is that the same "resulttotal" has been interpreted differently once as a variable and the second time as a value

hmmm.. are you under the impression that a variable and a value are two different things?

btw, i am pretty much ONLY a C language programmer, and the metatrader mql language is for all practical purposes a c language editor/compiler that has trading functions built into it.

is this concept of a value versus a variable a thing that you get from another language, perhaps python?

i am a self taught programmer, and so i probably approach things differently than will your typical university trained programmer..

when we have a variable named 'x', and we initialize it by saying "int x=1;", we are basically telling the computer to set aside a "box" in memory into which we can store a number by saying "x=20" and we can also request to print out that value by saying "Print(x);" which means to print the value that is contained in the box that is named "x".

does that help?

edit: also, let me see if i can explain something to you...

when we use the equals sign, you must understand that there is always some kind of variable name to the left of the equals sign, in your case resulttotal, and then you also have some kind of calculation on the right side of the equals sign..

RESULTTOTAL=1;

int the above example, the calculation on the right side is simply a number one, so there is not much of a calculation to be done, the result is ONE and value is assigned to the memory box that is named "RESULTTOTAL"..

if we say RESULTTOTAL=RESULTTOTAL +1, the calculation on the right side is RESULTTOTAL+1, and if RESULTTOTAL begins by containing a ONE, the outcome of the calculation will be TWO, and that number TWO will be stored in the memory box that is named RESULTTOTAL.

and now i will give you some sortof advanced programming shorthand...

when you want to increment(add one to something) a variable, you can say RESULTTOTAL=RESULTTOTAL+1; or you can use the shorthand for that which is RESULTTOTAL+=1;

decrementing a variable(subtracting one from something) like RESULTTOTAL=RESULT-1; can be written as RESULTTOTAL-=1;

additional examples are :

Inserted Code
 
resulttoal-=20; //subtract 20 from resulttotal
 
resulttotal+=100; //add 100 to resulttotal
 
//this following example is really useless, but i will show you anyways..
 
resulttotal-=resulttotal;  //resulttotal will always contain zero after this operation.
 
resulttotal+=resulttotal; //doubles resulttotal
 
resulttotal*=3; //multiplies resulttotal X 3
 
resulttotal/=15; //divides resulttotal by 15
 
resulttotal*=((resulttotal*x)+Y);
 
the above exampe multiples resulttotal*x and then adds Y to that value and then
multiplies that with resulttotal and stores that final result in the memory box that
is named "resulttotal".
 
 
ok, now let me show to you a fairly advanced way to use a "for loop without parameters"
 
for(;;)
{
//this will execute forever and ever.
}
 
or, another way is to do this:
 
int x=0;
for(;;)
{
Print("x=",x)
 
x++; //same as saying x=x+1;
if(x>10) break;
}
  • #5
  • Mar 11, 2021 5:15pm Mar 11, 2021 5:15pm
Quoting jmoreno
{quote} hmmm.. are you under the impression that a variable and a value are two different things?
yes, is not variable is space to store a data in while the value is constant because it is value
  • #6
  • Edited 5:29pm Mar 11, 2021 5:16pm | Edited 5:29pm
Quoting MichaelMano
{quote} I understand your explanation perfectly sir, what I am struggling with sir, is that the same "resulttotal" has been interpreted differently once as a variable and the second time as a value, which I do not understand so if we are saying resulttotal = resulttotal +i; here the "resulttotal" on the left side has been interpreted as a variable while "resulttotal" on the right side has been interpreted as value although both on the same line both same-named, and that is my question how the system could distinguish between these 2 please let me...
In every mature language statements are split into expressions and then most simple expressions are evaluated from right to left. How statements and expressions are split into sub-expressions depends on the operators between them and the precendence rules of operators. Example
Inserted Code
resultaverage = resulttotal / totalbar;

The first split is caused by the equal sign "=", an assignment. Splitting the statement into a left-side assignment and a right-side expression. An assignment is always evaluated from right to left which means the expression on the right side is evaluated first and the result is assigned to the left-side operand (here a variable).

So first we evaluate "resulttotal / totalbar" which is a simple divison. The result is kept in memory, to be more exact: in a register of the CPU.

Then the result is assigned to the operand on the left-side. It doesn't matter wether the same variable was already used somewhere else (the right side). All that matters is that the calculation result of the expression (now in the CPU register) is assigned to the variable on the left. This way you can calulate something and assign the result to a variable with the same name.

Why is it assigned? An expression "does" something with the operands, and it "returns" something. In other words: an expression "evaluates to" something, and if this "something" is on the right side of an assignment the "something" is assigned to the left-side operand, e.g. "a = (5+3)/2". The right side evaluates to a result (4 in this case) and returns at the same time these "4". The evaluation result then gets assigned to the left-side operand and, voila, variable "a" becomes "4".

Another example:
Inserted Code
resultaverage++;

Here we have only one expression, one operand and an operator. The "operator" does something to the "operands" depending on the type of operator and the operands. E.g. there is an addition operator "+" which works on two operands (left- and right-side), and there is an increment operator "++" which does something only to the left operand. Write "resultaverage ++" (with spaces in between) and it will do exactly the same because "++" only cares about what's on the left side.

So it goes on and there are countless operators and expression types wich all have their own rules to get logically resolved in the program flow.

@see https://www.mql5.com/en/docs/basis/operations
It takes blood, sweat and enough tears to wash away the blood.
  • #7
  • Mar 11, 2021 6:20pm Mar 11, 2021 6:20pm
Quoting MichaelMano
{quote} yes, is not variable is space to store a data in while the value is constant because it is value
variables are not typically thought of as "constants" in C language.

again, i am a self taught programmer, and i pretty much never use CONSTANTS, and cant really remember how to even define them, but it is something like this:

const int x=43; //something like that...

in C, and probably the same is true for the metatrader mql4 language, a variable can be used just the same as a constant..

instead of using "const int x=43;", you could just as easily say "int x=43;".

using a const is simply a way to define a value that is referred to by using a variable name AND IT IS NOT ALLOWED TO CHANGE THAT VALUE ANYWHERE IN YOUR CODE.. IT IS BASICALLY A SAFETY MECHANISM, WHICH ISNT REALLY NEEDED IF YOU ARE SIMPLY CAREFUL ABOUT HOW YOU WRITE YOUR CODE.

a variable, such as "resulttotal" is simply a name that refers to a memory location where a number is stored.

if i say "int X =1;", a memory location is reserved for which we will now talk about that memory location by it's name instead of referring to it by an actual memory location.

to say "x++" simply increments the value that is stored in the value at the location that is named "x".

Inserted Code
the following statements are the same:
 
x++;
x+=1;
x=x+1;
 
and the following, likewise, accomplish the same thing also:
 
x--;
x-=1;
x=x-1;
 
 
if my age is 58, i might say this:
 
int age=58;
 
and then on my next birthday, i might do any of the following:
 
age++;
age=age+1;
age+=1;
 
//rarely do we get younger...
 
age--;
age=age-1;
age-=1;
  • #8
  • Mar 12, 2021 6:11am Mar 12, 2021 6:11am
Quoting jmoreno
{quote} variables are not typically thought of as "constants" in C language. again, i am a self taught programmer, and i pretty much never use CONSTANTS, and cant really remember how to even define them, but it is something like this: const int x=43; //something like that... in C, and probably the same is true for the metatrader mql4 language, a variable can be used just the same as a constant.. instead of using "const int x=43;", you could just as easily say "int x=43;". using a const is simply a way to define a value that is referred to by using...
Thank you sir for your help, very helpful.
  • #9
  • Last Post: Mar 12, 2021 6:13am Mar 12, 2021 6:13am
Quoting emmzett
{quote} In every mature language statements are split into expressions and then most simple expressions are evaluated from right to left. How statements and expressions are split into sub-expressions depends on the operators between them and the precendence rules of operators. Example resultaverage = resulttotal / totalbar; The first split is caused by the equal sign "=", an assignment. Splitting the statement into a left-side assignment and a right-side expression. An assignment is always evaluated from right to left which means the expression...
I am enlighted, you break it down perfectly, thank you so much
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