1. introduction
2.arithmetic
3. if-else - CLICK
4.loop
5. List: click
6. CBCS university assignments CLICK
7. Read value from user:
1. BIRYINI IS A FOOD.
QUESTION:?
A) IS BIRIYANI A FOOD?
B) IS MOMO A FOOD?
CLICK HERE
2.
BIRYINI IS A FOOD.
MOMO IS A FOOD.
QUESTION:?
A) HOW MANY FOODS?
B) IF ALL FOODS ARE MEAL , THEN DISPLAY ALL MEALS.
CLICK HERE
3.
BIRYINI IS A FOOD.
MOMO IS A FOOD.
BIRIYANI IS A LUNCH.
QUESTION:?
A) WHICH ITEMS ARE IN LUNCH?
CLICK HERE
. Print "Hello World"
Description
This program prints the message Hello World on the screen.
Program
Run
Output
Explanation
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hello is a predicate.
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write() displays text on the screen.
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:- means "is defined as".
2. Input Your Name and Print It
Description
This program accepts a user's name and prints a greeting.
Program
Run
Sample Input
Output
Explanation
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read(Name) reads input from the keyboard.
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The entered value is stored in variable
Name.
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write(Name) displays the stored value.
3. Input Two Numbers and Display Them
Description
This program reads two numbers and displays them.
Program
Run
Sample Input
Output
Explanation
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A stores the first number.
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B stores the second number.
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nl prints a new line.
4. Input a Number and Print Its Square
Description
This program accepts a number and prints its square.
Program
Run
Sample Input
Output
Explanation
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read(N) reads the number.
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is evaluates arithmetic expressions.
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S stores the square of N.
5. Input Age and Display Eligibility to Vote
Description
This program checks whether a person is eligible to vote.
Program
Run
Sample Input
Output
Sample Input
Output
Explanation
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>= checks if the age is 18 or more.
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< checks if the age is less than 18.
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Based on the condition, the appropriate message is printed.
Prolog Operators with Examples
Operators in Prolog are symbols used to perform arithmetic calculations, comparisons, logical operations, and term matching.
1. Arithmetic Operators
These operators perform mathematical calculations.
| Operator | Meaning | Example | Result |
|---|
+ | Addition | X is 10 + 5. | X = 15 |
- | Subtraction | X is 10 - 5. | X = 5 |
* | Multiplication | X is 10 * 5. | X = 50 |
/ | Division | X is 10 / 5. | X = 2.0 |
// | Integer Division | X is 10 // 3. | X = 3 |
mod | Remainder | X is 10 mod 3. | X = 1 |
** | Power | X is 2 ** 3. | X = 8.0 |
Example Program
Output
2. Arithmetic Comparison Operators
These operators compare numeric values.
| Operator | Meaning | Example | Result |
|---|
> | Greater than | 10 > 5 | True |
< | Less than | 5 < 10 | True |
>= | Greater than or equal | 10 >= 10 | True |
=< | Less than or equal | 5 =< 8 | True |
=:= | Arithmetic equality | 5+5 =:= 10 | True |
=\= | Arithmetic inequality | 10 =\= 5 | True |
Example
Output
3. Unification Operators
These operators compare or assign terms.
| Operator | Meaning | Example |
|---|
= | Unify two terms | X = 10. |
\= | Not unifiable | 10 \= 20. |
== | Exactly identical | 10 == 10. |
\== | Not identical | 10 \== 20. |
Example
Output
4. Logical Operators
These operators combine conditions.
| Operator | Meaning | Example |
|---|
, | AND | A > 5, A < 20 |
; | OR | A = 5 ; A = 10 |
\+ | NOT | \+ (5 > 10) |
Example
Output
5. Assignment Operator (is)
The is operator evaluates an arithmetic expression and assigns the result to a variable.
Syntax
Example
Output
6. Example Program Using Multiple Operators
Sample Run
Summary of Prolog Operators
| Category | Operators |
|---|
| Arithmetic | +, -, *, /, //, mod, ** |
| Comparison | >, <, >=, =<, =:=, =\= |
| Unification | =, \=, ==, \== |
| Logical | , (AND), ; (OR), \+ (NOT) |
| Assignment | is |
IF-ELSE in Prolog
Unlike languages such as C, C++, or Java, Prolog does not have a traditional if-else statement. Instead, it uses the If-Then-Else operator (-> ;).
Syntax
Meaning
-
Condition → Checks the condition.
-
-> → Means THEN.
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; → Means ELSE.
Example 1: Check Eligible to Vote
Program
Run
Sample Input
Output
Sample Input
Output
Example 2: Find Larger Number
Program
Sample Run
Example 3: Check Even or Odd
Program
Sample Output
Example 4: Find Positive or Negative
Program
Output
Example 5: Pass or Fail
Program
Output
Nested IF-ELSE Example (Grade Calculator)
Program
Sample Run
General Syntax
Difference Between C and Prolog IF-ELSE
| C/C++ | Prolog |
|---|
if(condition) | (Condition -> ...) |
else | ; |
{ } block | Parentheses ( ) |
Statement ends with ; | Predicate ends with . |
What is a List in Prolog?
A list is a collection of elements enclosed in square brackets [ ].
-
A list can contain numbers, atoms, variables, or even other lists.
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Elements are separated by commas.
Syntax
Examples
Characteristics of a List
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Ordered collection of elements.
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Elements are enclosed within
[ ].
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Elements are separated by commas.
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A list may contain duplicate values.
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Lists can contain different data types.
Example
Head and Tail of a List
A list consists of:
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Head → First element
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Tail → Remaining elements
Syntax
Example
Head
Tail
Example Program
Run
Output
Empty List
An empty list contains no elements.
Syntax
Example
Output
List Matching (Pattern Matching)
Prolog matches list elements using variables.
Example
Output
Check Membership using member/2
The member/2 predicate checks whether an element exists in a list.
Syntax
Example
Run
Output
Another Example
Output
Append Two Lists
The append/3 predicate joins two lists.
Syntax
Example
Output
Length of a List
The length/2 predicate counts the number of elements.
Example
Output
Reverse a List
The reverse/2 predicate reverses a list.
Example
Output
Sort a List
The sort/2 predicate arranges elements in ascending order.
Example
Output
Find Maximum Element
Output
Find Minimum Element
Output
Sum of List Elements
Output
Nested List
Lists can contain other lists.
Example
Another Example
Access Head and Tail
Output
Generate List Members
Output
Common Built-in List Predicates
| Predicate | Description | Example |
|---|
member/2 | Checks whether an element exists | member(5,[1,2,5]) |
append/3 | Joins two lists | append([1],[2],L) |
length/2 | Counts elements | length([1,2,3],N) |
reverse/2 | Reverses a list | reverse([1,2],R) |
sort/2 | Sorts elements | sort([4,2,1],L) |
max_list/2 | Finds the largest element | max_list([2,5,3],M) |
min_list/2 | Finds the smallest element | min_list([2,5,3],M) |
sum_list/2 | Calculates the sum of elements | sum_list([1,2,3],S) |
Advantages of Lists
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Easy to store multiple values.
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Dynamic size (can grow or shrink).
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Supports recursion efficiently.
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Useful for searching and pattern matching.
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Widely used in Artificial Intelligence and symbolic programming.
What is Cut (!)?
The Cut operator (!) is a special control operator in Prolog.
It is used to stop backtracking and prevent Prolog from searching for alternative solutions after the cut is reached.
Definition
The Cut (!) is a control operator that commits Prolog to the choices made before it and prevents further backtracking beyond that point.
Syntax
Why Do We Use Cut?
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Improves program efficiency.
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Stops unnecessary backtracking.
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Makes the program execute faster.
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Selects only one solution.
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Prevents Prolog from trying other rules.
How Cut Works
Without Cut
With Cut
Example 1: Simple Cut
Program
Run
Output
Explanation
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20 >= 15 is true.
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Prolog reaches
!.
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Backtracking stops.
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The second rule is ignored.
Example 2: Without Cut
Run
Output
Explanation
Since there is no Cut, Prolog also tries the second rule during backtracking.
Example 3: Check Positive Number
Run
Output
Another Run
Output
Example 4: Maximum of Two Numbers
Run
Output
Example 5: Grade Calculator
Run
Output
Example 6: Voting Eligibility
Run
Output
Example 7: Even or Odd
Run
Output
Cut with If-Then-Else
This example uses If-Then-Else (-> ;) and does not require Cut, because the conditional already commits to one branch.
Types of Cut
1. Green Cut
A Green Cut improves efficiency without changing the logical meaning of the program.
Example
Purpose: Prevents unnecessary backtracking while preserving correct results.
2. Red Cut
A Red Cut changes the logical behavior of the program. Using or removing it may change the answers produced.
Example
Here, the cut commits to the first matching rule, affecting how later rules are considered.
Advantages of Cut
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Stops unnecessary backtracking.
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Makes execution faster.
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Improves program efficiency.
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Reduces memory usage.
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Produces a single desired solution.
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Simplifies control flow in some programs.
Disadvantages of Cut
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Can make programs harder to understand.
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May change the logical meaning if used incorrectly.
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Makes debugging more difficult.
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Overuse can reduce program readability.
Difference Between Cut and If-Else
Cut (!) | If-Then-Else (-> ;) |
|---|
| Stops backtracking | Selects one branch based on a condition |
| Used for execution control | Used for conditional decisions |
| Can affect later rule selection | Does not rely on multiple clauses |
| May improve efficiency | Improves readability for conditions |
Summary
| Symbol | Meaning |
|---|
! | Cut operator |
| Purpose | Stops backtracking |
| Benefit | Improves efficiency and selects a single solution |
| Types | Green Cut, Red Cut |
| Main Use | Control execution and avoid unnecessary alternative solutions |