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Short form of IF-statement:

if condition then
   some operator
...

some operator will be done if the condition is True. If the condition is False pascal will skip some operator.

E.g:

var a:=5;
if a > 7 then
   print(a-1)
print(a) 
// the value of a (5) will be displayed

The statements after the if statement will run regardless if the condition is true or false: 

print(a)

Full form of IF-statement:

The else statement runs a block of code if none of the conditions are True before this else statement:

if condition then
   operator1
else
   operator2

operator1 will be done if the condition is True; in this case operator2 will be not executed. If the condition is False pascal will skip operator1 and will execute operator2. Before else-block semicolon is not needed.

E.g:

var a:=5;
if a > 7 then
   print(a-1)
else
   print(a+1)
print(a) 
// at first the value of a+1 (6) will be displayed and then the value of a (5)

The semicolon before else is not needed!

Also there can be not one but two or more conditions. Each condition must be in round brackets.

E.g:

if(year<20) or (year>18) then 
    …
// if one of the conditions or both conditions are true then ...

After if-block and else-block may go not one but some operators. In this case we have to use begin..end block:

if condition then
begin
   operator1
   operator2
end
else
begin
   operator3
   operator4
end

The most popular errors:

You don't need to write semicolon before else.

Don't forget about begin..end in the cases when there is more than one operand after then or else.

Examples

• If the variable is odd or even:


• If the variable is not greater than 2:

How to Swap Values of Variables?

1 solution:

2 solution:

Tasks (if-statement)

Max points for all tasks = 4

1. {0.5 points}[task-01-if.pas] An integer is given. If it is positive then add 1 to it. Output the result.

Example:

-3 >>> -3
 0 >>>  0
 1 >>>  2
 5 >>>  6

2. {0.5 points}[task-02-if.pas] An integer is given. If it is even number then myltiply it by 10. Output the result.

Example:

2 >>> 20
1 >>>  1
-10 >>> -100

3. {0.5 points}[task-03-if.pas] An integer is given. If it is even number then myltiply it by 3, if it is not even then devide it by 3. Output the result.

Example:

4 >>> 12
9 >>>  3
-10 >>> -30

4. {0.8 points}[task-04-if.pas] An integer is given. If it is positive then add 1 to it; otherwise subtract it by 2. Output the number at the end of the program.

Example:

-3 >>> -5
 0 >>> -2
 1 >>>  2
 5 >>>  6

5. {0.8 points}[task-05-if.pas] An integer is given (the age of a person). If it is grater than or equal to 18 then output "you can watch this movie"; if the number is less than 10 then output "you should watch the cartoon". Otherwise output "you can take a walk".

Example:

18 >>> you can watch this movie
 8 >>> you should watch the cartoon
 15 >>>  you can take a walk

6. {0.8 points}[task-06-if.pas] Student has got a mark. If it is 2 mark then the program has to output "it's very bad"; if it is 3 - program has to output "it's bad"; if it is 4 - "it's good", in the case of 5 - "it's excellent", otherwise - "such marks do not exist" . 

Example:

2 >>> "it's very bad"
4 >>> "it's good"

7. {0.8 points}[task-07-if.pas]The program must request the time of day in hours (from 1 up to 24). Depending on the time entered, display a message indicating what time of day the entered hour belongs to (midnight (24), night (1-4), morning (5-11), day (12-16), evening (17-13)).

Example:

2 >>> "night"
24 >>> "midnight"

8. {0.8 points}[task-08-if.pas] Two integer values are given: for variables A and B. Assign a sum of these values to each variable if their values are not equal; otherwise (if equal) assign zero to the variables. Output new values of variables A and B.

Example:

A = -6, B = 10 >>> A = 4, B = 4
A =  2, B =  2 >>> A = 0, B = 0
A =  0, B =  0 >>> A = 0, B = 0

Check. Check the correctness of your program with at least two input sets: for the same and different values of the variables A, B. Give the log of the program with these sets in the form of a comment.

9. {0.3 points}[task-09-if.pas] Two integer values are given: for variables A and B. Swap the values of the variables and output them.

Example:

A = -6, B = 10 >>> A = 10, B = -6

10. {0.5 points}[task-10-if.pas] Two integer values are given: for variables A and B. If the value of A is greater than the value of B - swap the values of the variables and output them.

Example:

A = 6, B = 2 >>> A = 2, B = 6