combine two or more conditions in one if statement

Question

Can we combine two or more conditions in one if statement? I know that in C# we can combine two or more conditions in an IF statement. Can we do it in Delphi? I have to check whether the user entered a value for the three Edit controls in the form. Thanks for all the help

Accepted Answer

The general form of conditional statement is : IF "Logical expression" THEN ...ELSE ... The "Logical expression" is any boolean expression. A boolean expression is an expression can be evaluated as TRUE or FALSE. A boolean expression can be constructed using comparison operators and boolean operators. Comparison operators: ``` = equals <> not equals > greater than >= greater than or equals < less than <= less than or equals ``` Set Comparison operators: ``` = equals <= returns true, if set1 is a subset of set2 >= returns true, if set1 is a superset of set2 in returns true, if an element is in the set ``` Boolean operators: ``` AND logical and OR logical or NOT logical not XOR logical exclusive disjucntion ``` Examples: ``` IF A = 10 THEN ... IF A >= B THEN ... IF C or D THEN ... (Note: C and D have to be logical, i.e. TRUE or FALSE) IF NOT E THEN ... (Note: E has to be logical, i.e. TRUE or FALSE) ``` C, D and E can be replace with any logical expression, for example: ``` IF (edit1.text = '') OR ( ISEMPTY( edit2.text ) ) THEN ... IF NOT checkbox1.checked THEN ... ``` Note that logical expression can be constructed from simpler logical expressions by using boolean operators, for examples: ``` IF ( A = 10 ) AND ( A >= B ) THEN ... IF NOT ( ( A = 10 ) AND ( A >= B ) ) THEN ... ``` Common mistake in writing logical expression is not paying attention of operator precedence (which operator evaluated first). The boolean operators have higher precedence than comparison operators, for example: ``` IF A = 10 OR A >= B THEN ... ``` The above is wrong because Delphi tries to evaluate `10 OR A` first, instead of `A = 10`. If A itself is not a logical expression, then error occurs. The solution is by using brackets, so the above IF...THEN...should be written as: `IF (A = 10) OR (A >= B) THEN ...` For checking 3 edit controls, the conditional statement becomes: `IF ( Edit1.text <> '' ) AND ( Edit2.text <> '' ) AND ( Edit3.text <> '' ) THEN ...` Note: Slightly off topic, but related. Free components TJvValidators, TJvValidationSummary and TJvErrorIndicator from Jedi JVCL project provide a nice validation mechanism.

combine two or more conditions in one if statement

Solution

Problem