Chapter 2a - Conditionals & Loops

If / Else

Use if to run code only when a condition is true. else if and else handle alternative cases.

int score = 75;

if (score >= 90) {
    cout << "Grade: A" << endl;
} else if (score >= 80) {
    cout << "Grade: B" << endl;
} else if (score >= 70) {
    cout << "Grade: C" << endl;
} else {
    cout << "Grade: F" << endl;
}

Comparison Operators

Operator	Meaning	Example
==	Equal to	a == b
!=	Not equal to	a != b
<	Less than	a < b
>	Greater than	a > b
<=	Less than or equal	a <= b
>=	Greater than or equal	a >= b

= vs ==

= assigns a value. == compares two values. Mixing them up is one of the most common C++ bugs.

Logical Operators

Combine multiple conditions with && (AND), || (OR), ! (NOT).

int age = 20;
bool hasId = true;

if (age >= 18 && hasId) {
    cout << "Access granted." << endl;
}

bool isWeekend = false;
bool isHoliday = true;

if (isWeekend || isHoliday) {
    cout << "No school today!" << endl;
}

🧪 Try conditionals

Press Run, then type a number and press Enter.

Challenge: sign of a number

Finish signWord so it returns "positive", "negative", or "zero". Use if / else if / else, not switch.

Input	Return
5	positive
-3	negative
0	zero

---

Switch Statement

switch is a cleaner alternative to long if/else if chains when checking a single variable against exact values.

int day = 3;

switch (day) {
    case 1:
        cout << "Monday" << endl;
        break;
    case 2:
        cout << "Tuesday" << endl;
        break;
    case 3:
        cout << "Wednesday" << endl;
        break;
    default:
        cout << "Another day" << endl;
        break;
}

Don't forget break!

Without break, execution "falls through" to the next case. This is almost always a bug unless intentional.

🧪 Try switch

Enter a day number 1–7.

Challenge: drink menu

Finish drinkName so it returns a string from an integer order. Use switch, not if. A hidden main reads one number and prints your return value.

Input	Return
1	coffee
2	tea
3	water
anything else	unknown

---

For Loop

Use a for loop when you know how many times to repeat.

// Syntax: for (init; condition; update)
for (int i = 0; i < 5; i++) {
    cout << "i = " << i << endl;
}

i = 0
i = 1
i = 2
i = 3
i = 4

🧪 Loop examples

Challenge: sum with for

Finish sumTo so it returns 1 + 2 + … + n. Use a for loop, not while.

Input	Return
5	15
1	1
10	55

Nested For Loops

Loops can be placed inside other loops. The inner loop completes fully for each step of the outer loop.

for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= 3; col++) {
        cout << row << "x" << col << "=" << row * col << "  ";
    }
    cout << endl;
}

1x1=1  1x2=2  1x3=3
2x1=2  2x2=4  2x3=6
3x1=3  3x2=6  3x3=9

🧪 Nested loops

---

While Loop

Use while when you want to repeat as long as a condition holds, and you don't know the count upfront.

int count = 0;
while (count < 5) {
    cout << "count = " << count << endl;
    count++;
}

🧪 While loop with user input

Guess until you get 42. Type a number and press Enter after each prompt.

Challenge: countdown with while

Finish countDown so it prints n down to 1, separated by spaces. Use while, not for.

Input	Output
5	5 4 3 2 1
1	1

---

Do-While Loop

do-while always runs the body at least once, then checks the condition.

int n;
do {
    cout << "Enter a positive number: ";
    cin >> n;
} while (n <= 0);

cout << "You entered: " << n << endl;

Loop type	Checks condition	Use when
for	Before each iteration	Count is known
while	Before each iteration	Count is unknown
do-while	After each iteration	Body must run at least once

🧪 Try do-while

Enter a non-positive number first (like -3), then a positive one.

Challenge: first positive with do-while

Finish firstPositive so it reads integers until one is greater than 0, then returns that value. Use do / while. Hidden tests send several lines of input.

Input lines	Return
-2 then 0 then 4	4
7	7

---

Break and Continue

break exits the loop immediately. continue skips the rest of the current iteration and moves to the next.

// Skip multiples of 3, stop at 10
for (int i = 1; i <= 15; i++) {
    if (i == 10) break;
    if (i % 3 == 0) continue;
    cout << i << " ";
}
// Output: 1 2 4 5 7 8

🧪 Break and continue

Challenge: skip threes, then break

Finish printSkipThrees. Loop i from 1 to 20. break when i equals limit. continue when i is a multiple of 3. Print the other numbers with a space after each.

Input (limit)	Output
10	1 2 4 5 7 8
5	1 2 4

---

Exercises

Activity: FizzBuzz

Print the numbers 1 to 100. For multiples of 3 print "Fizz", for multiples of 5 print "Buzz", for multiples of both print "FizzBuzz".

1
2
Fizz
4
Buzz
Fizz
7
...

💡 Hint

Check i % 3 == 0 && i % 5 == 0 first (before checking each individually), or the combined case will never be reached.

📒 Solution