X++ conditional statements

Άρθρο
08/12/2022

This article describes conditional statements in X++. The conditional statements are if, if...else, switch, and the ternary operator (?). You use conditional statements to specify whether a block of code is executed. Different conditional statements offer advantages in different situations.

if and if...else statements

The if statement evaluates a conditional expression, and then executes a statement or a set of statements if the conditional expression is evaluated as true. You can use the else clause to provide an alternative statement or set of statements that is executed if the condition is evaluated as false. The syntax for an if...else statement is:

if ( expression ) statement [else statement ]

In this syntax, both occurrences of statement can be compound statements (statements enclosed in braces). The expression in the parentheses (the conditional expression) can be any valid expression that is evaluated as true or false. All numbers except 0 (zero) are true. All non-empty strings are true. You can nest if statements. However, if the nesting of if statements becomes too deep, you should consider using a switch statement instead.

Examples of if and if...else statements

// if statement
if (a > 4)
{
   info("a is greater than 4");
}

// if... else statement 
if (a > 4)
{
   info("a is greater than 4");
}
else
{
   info("a is less than or equal to 4");
}

switch statements

The switch statement is a multibranch language construct that has the same behavior as nested if. The expression of the switch statement is evaluated and checked against each case value. The case values must be constants that the compiler can evaluate.

If a case constant matches the switch expression, the case statement is executed.
If the case contains a break statement, the program then jumps out of the switch.
If the case doesn't contain a break statement, the program continues and executes the next case statements.
If no matches are found, the default statement is executed.
If there are no matches and no default statement, none of the statements inside the switch statement are executed.

Here is the syntax for a switch statement:

switch ( expression ) { { case } [default: statement ] }

The syntax for a case statement is:

case expression { , expression } : statement

In the syntax for both a switch statement and a case statement, every occurrence of statement can be replaced with a block of statements by enclosing the block in braces ({}).

Examples of switch statements

When you include the break keyword in a switch statement, the execution of the case branch terminates, and the statement following the switch is executed. As shown in the following example, if the Debtor account number is 1000, the program executes "do something", and then continues execution after the switch statement.

switch (Debtor.AccountNo)
{
    case "1000":
        // do something
        break;
    case "2000":
        // do something else
        break;
    default:
        // default statement
        break;
}

The following code example makes the execution drop through the first case branch by omitting a break statement. If x is 10, b is assigned to a, and d is assigned to c. If x is 11, d is assigned to c. If x is 12, f is assigned to e.

 switch (x)
 {
     case 10:
         a = b;
     case 11:
         c = d;
         break;
     case 12:
         e = f;
         break;
 }

If you do not use the break statement, the program flow in the switch statement continues into the next case. Code segments A and B have the same behavior.

// Code segment A (break omitted)
case 13:
case 17:
case 21:
case 500:
    info("g");
    break;

// Code segment B (the values are comma-delimited)
case 13, 17, 21, 500;
    info("g");
    break;

Ternary operator (?)

The ternary operator (?) is a conditional statement that is resolved to one of two expressions. The result can be assigned to a variable. By contrast, an if statement provides conditional branching of the program flow but can't be assigned to a variable. Here is the syntax for the ternary operator:

expression1 ? expression2 : expression3

In this syntax, expression1 must return a value of true or false. If expression1 is true, the whole ternary statement returns expression2. Otherwise, the statement returns expression3. Both expression2 and expression3 must have the same type.

Examples of the ternary operator (?)

The following code example returns one of two strings based on a Boolean return value from a method call. The Boolean expression indicates whether the CustTable table has a row with a RecId field value of 1. If this Boolean expression is true (meaning RecId != 0), found is assigned to result. Otherwise, the alternative not found is assigned to result.

result = (custTable::find("1").RecId) ? "found" : "not found";

You can nest statements with the ternary operator. The following example assigns one of three values to level based on the value of x.

int x = 1001;
str level = x <= 1000 ? "A" : (x <= 2000 ? "B" : "C");
info(level);
// Output is "B".

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