Making Decisions — If, Else, Comparisons

Programs need to think — to do different things based on conditions. This is called control flow.

Comparisons

Before decisions, you need to compare values:

Operator	Meaning	Example	Result
==	Equal to	5 == 5	true
!=	Not equal	5 != 3	true
>	Greater than	10 > 5	true
<	Less than	3 < 7	true
>=	Greater or equal	5 >= 5	true
<=	Less or equal	4 <= 4	true

let age = 20;

print(age == 20);    // true
print(age != 20);    // false
print(age >= 18);    // true
print(age < 18);     // false

Output:

true
false
true
false

Note: Use == for comparison, = is for assignment!

The if Statement

Run code only if a condition is true:

let score = 85;

if (score >= 60) {
    print("You passed!");
}

Output:

You passed!

If condition is false, the block is skipped:

let score = 45;

if (score >= 60) {
    print("You passed!");
}
print("Done checking.");  // Always runs

Output:

Done checking.

The else Block

Run alternative code when condition is false:

let score = 45;

if (score >= 60) {
    print("Pass");
} else {
    print("Fail");
}

Output:

Fail

The elif Chain

Check multiple conditions in order:

let score = 82;

if (score >= 90) {
    print("Grade: A");
} elif (score >= 80) {
    print("Grade: B");
} elif (score >= 70) {
    print("Grade: C");
} elif (score >= 60) {
    print("Grade: D");
} else {
    print("Grade: F");
}

Output:

Grade: B

Key: Only the first matching block runs. Order matters!

Logical Operators

Combine multiple conditions:

Operator	Name	Example	True When
&&	AND	a > 0 && a < 100	Both true
`		`	OR
!	NOT	!(age >= 18)	Condition is false

let age = 25;
let has_ticket = true;

// AND - both must be true
if (age >= 18 && has_ticket) {
    print("Entry allowed");
}

// OR - at least one true
let is_student = false;
let is_senior = false;
if (is_student || is_senior) {
    print("Discount applies");
}

// NOT - invert
if (!(age >= 18)) {
    print("Minor");
}

Output:

Entry allowed

Nested Conditions

Conditions inside conditions:

let user = "admin";
let logged_in = true;

if (logged_in) {
    if (user == "admin") {
        print("Welcome, Administrator!");
    } else {
        print("Welcome, User!");
    }
} else {
    print("Please log in first");
}

Output:

Welcome, Administrator!

Practical Examples

Example 1: Number Guessing Game

let secret = 42;
let guess = 50;

if (guess == secret) {
    print("Correct! You win!");
} elif (guess > secret) {
    print("Too high! Try lower.");
} else {
    print("Too low! Try higher.");
}

Output:

Too high! Try lower.

Example 2: Login System

let username = "alice";
let password = "secret123";
let input_user = "alice";
let input_pass = "wrongpass";

if (username == input_user && password == input_pass) {
    print("Login successful!");
} elif (username != input_user) {
    print("Invalid username");
} else {
    print("Incorrect password");
}

Output:

Incorrect password

Example 3: Temperature Advisor

let temp = 15;  // Celsius

if (temp < 0) {
    print("Freezing! Wear heavy coat.");
} elif (temp < 10) {
    print("Cold. Wear jacket.");
} elif (temp < 20) {
    print("Cool. Light sweater.");
} elif (temp < 30) {
    print("Nice! T-shirt weather.");
} else {
    print("Hot! Stay hydrated.");
}

Output:

Cool. Light sweater.

Example 4: Simple Calculator

let a = 10;
let b = 5;
let op = "/";

if (op == "+") {
    print("Result:", a + b);
} elif (op == "-") {
    print("Result:", a - b);
} elif (op == "*") {
    print("Result:", a * b);
} elif (op == "/") {
    if (b != 0) {
        print("Result:", a / b);
    } else {
        print("Error: Cannot divide by zero!");
    }
} else {
    print("Unknown operator:", op);
}

Output:

Result: 2

Ternary Expression (One-Liner)

For simple choices, use the ternary operator:

let age = 20;
let status = (age >= 18) ? "Adult" : "Minor";
print(status);    // Adult

let score = 85;
let result = (score >= 60) ? "Pass" : "Fail";
print(result);    // Pass

Output:

Adult
Pass

Syntax: condition ? value_if_true : value_if_false

Truthy and Falsy Values

In conditions, these values are falsy (act like false):

Value	Type
false	Boolean
0	Number
""	Empty string
null	Null

Everything else is truthy:

let values = [1, "hello", true, -5, [1], {a:1}];

for v in values {
    if (v) {
        print(v, "is truthy");
    }
}

let falsy = [0, "", false, null];
for v in falsy {
    if (!v) {
        print(v, "is falsy");
    }
}

Output:

1 is truthy
hello is truthy
true is truthy
-5 is truthy
[1] is truthy
{a: 1} is truthy
0 is falsy
 is falsy
false is falsy
null is falsy

Common Patterns

Guard Clause (Return Early)

fn process(user) {
    // Check invalid first, exit early
    if (!user) {
        print("No user provided");
        return;
    }
    if (!user.active) {
        print("User not active");
        return;
    }
    
    // Main logic here
    print("Processing:", user.name);
}

Range Check

let x = 50;

if (x >= 0 && x <= 100) {
    print("In range 0-100");
}

// Or
if (0 <= x && x <= 100) {  // Works too
    print("In range");
}

Output:

In range 0-100
In range

Default Value

let input = null;
let value = (input != null) ? input : "default";
print(value);    // default

Output:

default

Quick Reference

Task	Code
Simple if	if (cond) { }
If-else	if (cond) { } else { }
If-elif-else	if (c1) { } elif (c2) { } else { }
AND	a && b
OR	a || b
NOT	!a
Ternary	cond ? a : b

Practice Exercise

Create grade_calculator.adesh:

fn get_grade(score) {
    if (score >= 90) return "A";
    if (score >= 80) return "B";
    if (score >= 70) return "C";
    if (score >= 60) return "D";
    return "F";
}

let scores = [95, 87, 72, 65, 58, 100];

for s in scores {
    print("Score:", s, "→ Grade:", get_grade(s));
}

Output:

Score: 95 → Grade: A
Score: 87 → Grade: B
Score: 72 → Grade: C
Score: 65 → Grade: D
Score: 58 → Grade: F
Score: 100 → Grade: A

Summary

✅ You learned:

• Comparison operators: ==, !=, >, <, >=, <=
• if, elif, else for branching
• Logical operators: && (and), || (or), ! (not)
• Nested conditions
• Ternary operator for one-liners
• Truthy/falsy values
• Guard clause pattern

Next Step

Now let's repeat actions automatically with loops! Continue to Loops →