Hi folks,

Today we will study -what I consider it- the most important MQL4 lesson.

Loops & Decisions

for Loop
while loop
if statement
if..else statement
switch statement


I hope you enjoy the lesson and waiting your comments.

Attached Files

Lesson5.pdf (70.7 KB, 5020 views)

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Senior MQL programmer:
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Just few questions.

for (int i=0; i>15; i++)
{
if (i==10)
break;
Print (i);
}

As I understand it starts at i=0 and will continue untill the i>15 is true but suddenly it will be stoped because i==10 should be break. Thus we will have the values from 0 to 10 only. Right?

1. It was example for Multistatement in Loops and we used braces (see example). What are the rules to use braces? ({)

2. As I understand i==10 in the example above is the test expression and we must use relation operators instead of simple assignment operators (=). So i==10 is right (because == is relation operator). I am right?

3. What is Print? Do we need to use/write Print in capital letter? Is it printing?
Will we use this "Print" when we will write EA or indicator?

4. Why everything is located like this? I changed the font size but in the example everything is located in some strage way, not the same as you described us in Format lesson that we may use any space etc. A lot of indentions and different indentions: { is located under f letter, i on the next line is using indention, break is under f, P in Print is under i (if) and so on. Do we need to do it? And what are the rules for that indentions?

You typed the example in wrong way, it must be like that:

for(int i=0;i<15;i++)
{
if((i==10)
break;
Print(i);
}

And it means the loop work every time the Test Expression i < 15 is true.
So, it starts at i=0 and will continue until the i<15 is false
In your example the loop will not work even for one time, because i will never be > 15.

This was an example of Break statement which will terminate the loop when i==10.


There are no rules of using braces, but you there are some tips:

1- Every opened brace ({) has to be matched with a close brace (}), or you will get an error.
2- There's no semi-colon after the braces.
3- You can use braces too in a single line statement to make your work tidy and readable.



Yes, you are Right, you can't use assignment operator in this case.
Just keep in your mind that == means the question Is Equal.

Print is MQL4 built-in function, Its job is printing anything you put inside its parentheses to the experts log (you will find it as a tab below the MetaTrader chart beside the Mailbox tab and before Journal tab).

And it must start with a capital latter, because as you said in the MQL4 Data types lesson the functions names [identifiers in general] are case sensitive, so you have to type it Print.

You can use any amount of spaces or tabs you want.
But, to make your code tidy, readable and it’s a recommended way to avoid bugs in your code. You have to use indentation like the above example.

__________________
Hope it helps !
Coders' Guru
Senior MQL programmer:
www.xpworx.com/custom.htm

I appreciate your taking the time to provide these tutorials. I haven't programmed in C since the 80's, so this is helping knock off some of the rust.

Not to be trite, but in your next rev of the tutorial, you might want to correct the statement below (it's in your reply above as well as on page 5 of the tutorial) in that the brackets/parenthesis for the 'if((i==10)...' are unbalanced.

Thanks again,

MarkC.

Hi, thanks for all your work.

After your flowchart in Lesson 5 you said:

int i;
int j;
for(i=0,j=0,i<15,i<;i++;j++)
Print(i);

Was the bold part here a typo or was that supposed to be there? I don't see any explanation of why it would be there and you specifically said you can only have one test expression right after this.
Your next example has the same thing as well.


int i;
for(i=15,i>0,i<,i--)
Print(i);

I'm guessing it's gotta just be a typo.

Please let me know, thanks.