They're all int. Why do I have to convert?

[helloea]

double b1[];
double b2[];
double b3[];
double b4[];
double b5[];
void OnStart()
  {
int a1=CopyOpen(Symbol(),PERIOD_M5,0,1,b1);
int a2=CopyOpen(Symbol(),PERIOD_M5,0,2,b2);
int a3=CopyOpen(Symbol(),PERIOD_M5,0,3,b3);
int a4=CopyOpen(Symbol(),PERIOD_M5,0,4,b4);
int a5=CopyOpen(Symbol(),PERIOD_M5,0,5,b5);
Print("copyopen_a1="+a1);
Print("copyopen_a2="+a2);
Print("copyopen_a3="+a3);
Print("copyopen_a4="+a4);
Print("copyopen_a5="+a5);
ArraySetAsSeries(b1,true);
ArraySetAsSeries(b2,true);
ArraySetAsSeries(b3,true);
ArraySetAsSeries(b4,true);
ArraySetAsSeries(b5,true);
ArrayPrint(b1);
ArrayPrint(b2);
ArrayPrint(b3);
ArrayPrint(b4);
ArrayPrint(b5);
  }

implicit conversion from 'number' to 'string'   
implicit conversion from 'number' to 'string'   
implicit conversion from 'number' to 'string'   
implicit conversion from 'number' to 'string'   
implicit conversion from 'number' to 'string'   

In addition, who determines the values of a1,a2,a3,a4, and a5?

[Chris70]

I guess the problem is: for an integer number a1 an expression like "copyopen_a1="+a1 means you're trying to add a number to a string. You can only add a string to a string (concatenation).

The Print function accepts a comma separated list of the arguments, so there's no need for this addition: Print("copyopen_a1=",a1); should work.

Use IntegerToString() for those cases where a conversion is really necessary.

[helloea]

Chris70:

I guess the problem is: for an integer number a1 an expression like "copyopen_a1="+a1 means you're trying to add a number to a string. You can only add a string to a string (concatenation).

The Print function accepts a comma separated list of the arguments, so there's no need for this addition: Print("copyopen_a1=",a1); should work.

Use IntegerToString() for those cases where a conversion is really necessary.

"Print (" copyopen_a1 =" + a1);"The output is all strings because the + is used.

"Print (" copyopen_a1 =", a1);"The output is "copyopen_a1=" is a string, a1 is an integer,

Did I know that right?

[Roman]

The Print function uses strings.

Therefore, all numeric values must be cast to the string type.

Print("copyopen_a1 = ", IntegerToString(a1));
Print("copyopen_a2 = ", IntegerToString(a2));
Print("copyopen_a3 = ", IntegerToString(a3));
Print("copyopen_a4 = ", IntegerToString(a4));
Print("copyopen_a5 = ", IntegerToString(a5));

Or

Print("copyopen_a1 = " + (string)a1);
Print("copyopen_a2 = " + (string)a2);
Print("copyopen_a3 = " + (string)a3);
Print("copyopen_a4 = " + (string)a4);
Print("copyopen_a5 = " + (string)a5);

[Marco vd Heijden]

Additionally the PrintFormat() function needs the types specifically.

https://www.mql5.com/en/docs/common/printformat

type #

Type specifier is the only obligatory field for formatted output.

Symbol	Type	Output Format
c	int	Symbol of short type (Unicode)
C	int	Symbol of char type (ANSI)
d	int	Signed decimal integer
i	int	Signed decimal integer
o	int	Unsigned octal integer
u	int	Unsigned decimal integer
x	int	Unsigned hexadecimal integer, using "abcdef"
X	int	Unsigned hexadecimal integer, using "ABCDEF"
e	double	A real value in the format [-] d.dddde[sign] ddd, where d - one decimal digit, dddd - one or more decimal digits, ddd - a three-digit number that determines the size of the exponent, sign - plus or minus
E	double	Similar to the format of e, except that the sign of exponent is output by upper case letter (E instead of e)
f	double	A real value in the format [-] dddd.dddd, where dddd - one or more decimal digits. Number of displayed digits before the decimal point depends on the size of number value. Number of digits after the decimal point depends on the required accuracy.
g	double	A real value output in  f or e format depending on what output is more compact.
G	double	A real value output in  F or E format depending on what output is more compact.
a	double	A real number in format [−]0xh.hhhh  p±dd, where h.hhhh – mantissa in the form of hexadecimal digits, using "abcdef", dd - One or more digits of exponent. Number of decimal places is determined by the  accuracy specification
A	double	A real number in format [−]0xh.hhhh  P±dd, where h.hhhh – mantissa in the form of hexadecimal digits, using "ABCDEF", dd - One or more digits of exponent. Number of decimal places is determined by the  accuracy specification
s	string	String output

Instead of PrintFormat() you can use  printf().