Operators and Control Flow¶

1. Arithmetic Operators¶

Basic Arithmetic Operators¶

Operator	Meaning	Example
`+`	Addition	`a + b`
`-`	Subtraction	`a - b`
`*`	Multiplication	`a * b`
`/`	Division	`a / b`
`%`	Modulus	`a % b`

#include <iostream>

int main() {
    int a = 17, b = 5;

    std::cout << "a + b = " << a + b << std::endl;  // 22
    std::cout << "a - b = " << a - b << std::endl;  // 12
    std::cout << "a * b = " << a * b << std::endl;  // 85
    std::cout << "a / b = " << a / b << std::endl;  // 3 (integer division)
    std::cout << "a % b = " << a % b << std::endl;  // 2

    return 0;
}

Integer Division vs Floating-Point Division¶

#include <iostream>

int main() {
    int a = 7, b = 2;

    // Integer division (decimal truncated)
    std::cout << "7 / 2 = " << a / b << std::endl;  // 3

    // Floating-point division
    std::cout << "7.0 / 2 = " << 7.0 / 2 << std::endl;  // 3.5
    std::cout << "(double)7 / 2 = " << static_cast<double>(a) / b << std::endl;  // 3.5

    return 0;
}

Increment and Decrement Operators¶

#include <iostream>

int main() {
    int a = 5;

    std::cout << "a = " << a << std::endl;    // 5
    std::cout << "++a = " << ++a << std::endl; // 6 (prefix: increment first)
    std::cout << "a++ = " << a++ << std::endl; // 6 (postfix: increment after)
    std::cout << "a = " << a << std::endl;    // 7

    return 0;
}

2. Assignment Operators¶

Compound Assignment Operators¶

#include <iostream>

int main() {
    int a = 10;

    a += 5;   // a = a + 5
    std::cout << "a += 5: " << a << std::endl;  // 15

    a -= 3;   // a = a - 3
    std::cout << "a -= 3: " << a << std::endl;  // 12

    a *= 2;   // a = a * 2
    std::cout << "a *= 2: " << a << std::endl;  // 24

    a /= 4;   // a = a / 4
    std::cout << "a /= 4: " << a << std::endl;  // 6

    a %= 4;   // a = a % 4
    std::cout << "a %= 4: " << a << std::endl;  // 2

    return 0;
}

3. 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 to	`a <= b`
`>=`	Greater than or equal to	`a >= b`

#include <iostream>

int main() {
    int a = 5, b = 10;

    std::cout << std::boolalpha;  // Output as true/false
    std::cout << "a == b: " << (a == b) << std::endl;  // false
    std::cout << "a != b: " << (a != b) << std::endl;  // true
    std::cout << "a < b: " << (a < b) << std::endl;    // true
    std::cout << "a > b: " << (a > b) << std::endl;    // false
    std::cout << "a <= b: " << (a <= b) << std::endl;  // true
    std::cout << "a >= b: " << (a >= b) << std::endl;  // false

    return 0;
}

4. Logical Operators¶

Operator	Meaning	Example
`&&`	AND	`a && b`
`\\|\\|`	OR	`a \\|\\| b`
`!`	NOT	`!a`

#include <iostream>

int main() {
    bool a = true, b = false;

    std::cout << std::boolalpha;
    std::cout << "a && b: " << (a && b) << std::endl;  // false
    std::cout << "a || b: " << (a || b) << std::endl;  // true
    std::cout << "!a: " << (!a) << std::endl;          // false
    std::cout << "!b: " << (!b) << std::endl;          // true

    // Compound conditions
    int age = 25;
    bool isStudent = true;

    bool discount = (age < 20) || isStudent;  // Student or under 20
    std::cout << "Discount applied: " << discount << std::endl;  // true

    return 0;
}

Short-circuit Evaluation¶

#include <iostream>

int main() {
    int x = 0;

    // &&: If first is false, second is not evaluated
    if (false && (++x > 0)) {
        // x is not incremented
    }
    std::cout << "x after &&: " << x << std::endl;  // 0

    // ||: If first is true, second is not evaluated
    if (true || (++x > 0)) {
        // x is not incremented
    }
    std::cout << "x after ||: " << x << std::endl;  // 0

    return 0;
}

5. Bitwise Operators¶

Operator	Meaning	Example
`&`	AND	`a & b`
`\\|`	OR	`a \\| b`
`^`	XOR	`a ^ b`
`~`	NOT	`~a`
`<<`	Left shift	`a << n`
`>>`	Right shift	`a >> n`

#include <iostream>

int main() {
    int a = 5;  // 0101
    int b = 3;  // 0011

    std::cout << "a & b = " << (a & b) << std::endl;  // 1 (0001)
    std::cout << "a | b = " << (a | b) << std::endl;  // 7 (0111)
    std::cout << "a ^ b = " << (a ^ b) << std::endl;  // 6 (0110)
    std::cout << "~a = " << (~a) << std::endl;        // -6

    std::cout << "a << 1 = " << (a << 1) << std::endl;  // 10 (1010)
    std::cout << "a >> 1 = " << (a >> 1) << std::endl;  // 2 (0010)

    return 0;
}

6. Ternary Operator¶

condition ? value_if_true : value_if_false

#include <iostream>

int main() {
    int a = 10, b = 20;

    // Alternative to if-else
    int max = (a > b) ? a : b;
    std::cout << "Maximum: " << max << std::endl;  // 20

    // String selection
    int score = 85;
    std::string result = (score >= 60) ? "Pass" : "Fail";
    std::cout << "Result: " << result << std::endl;  // Pass

    // Nested (be careful with readability)
    int num = 0;
    std::string sign = (num > 0) ? "positive" : (num < 0) ? "negative" : "zero";
    std::cout << "Sign: " << sign << std::endl;  // zero

    return 0;
}

7. if Statement¶

Basic if Statement¶

#include <iostream>

int main() {
    int age = 18;

    if (age >= 18) {
        std::cout << "You are an adult." << std::endl;
    }

    return 0;
}

if-else Statement¶

#include <iostream>

int main() {
    int score = 75;

    if (score >= 60) {
        std::cout << "Pass" << std::endl;
    } else {
        std::cout << "Fail" << std::endl;
    }

    return 0;
}

if-else if-else Statement¶

#include <iostream>

int main() {
    int score = 85;

    if (score >= 90) {
        std::cout << "A" << std::endl;
    } else if (score >= 80) {
        std::cout << "B" << std::endl;
    } else if (score >= 70) {
        std::cout << "C" << std::endl;
    } else if (score >= 60) {
        std::cout << "D" << std::endl;
    } else {
        std::cout << "F" << std::endl;
    }

    return 0;
}

Variable Declaration in if Statement (C++17)¶

#include <iostream>
#include <map>
#include <string>

int main() {
    std::map<std::string, int> scores = {{"Alice", 90}, {"Bob", 85}};

    // C++17: Variable declaration in if statement
    if (auto it = scores.find("Alice"); it != scores.end()) {
        std::cout << "Alice's score: " << it->second << std::endl;
    }

    return 0;
}

8. switch Statement¶

Basic switch Statement¶

#include <iostream>

int main() {
    int day = 3;

    switch (day) {
        case 1:
            std::cout << "Monday" << std::endl;
            break;
        case 2:
            std::cout << "Tuesday" << std::endl;
            break;
        case 3:
            std::cout << "Wednesday" << std::endl;
            break;
        case 4:
            std::cout << "Thursday" << std::endl;
            break;
        case 5:
            std::cout << "Friday" << std::endl;
            break;
        case 6:
        case 7:
            std::cout << "Weekend" << std::endl;
            break;
        default:
            std::cout << "Invalid value" << std::endl;
    }

    return 0;
}

Fall-through (Intentional Omission)¶

#include <iostream>

int main() {
    char grade = 'B';

    switch (grade) {
        case 'A':
        case 'B':
        case 'C':
            std::cout << "Pass" << std::endl;
            break;
        case 'D':
        case 'F':
            std::cout << "Fail" << std::endl;
            break;
        default:
            std::cout << "Invalid grade" << std::endl;
    }

    return 0;
}

switch Statement Cautions¶

// switch only works with integral types, character types, and enums
// Strings are not allowed (in C++)

// Variable declaration requires braces
switch (value) {
    case 1: {
        int x = 10;  // Scope defined with braces
        // ...
        break;
    }
    case 2:
        // ...
        break;
}

9. for Loop¶

Basic for Loop¶

#include <iostream>

int main() {
    // Print 1 to 5
    for (int i = 1; i <= 5; i++) {
        std::cout << i << " ";
    }
    std::cout << std::endl;  // 1 2 3 4 5

    return 0;
}

Reverse for Loop¶

#include <iostream>

int main() {
    for (int i = 5; i >= 1; i--) {
        std::cout << i << " ";
    }
    std::cout << std::endl;  // 5 4 3 2 1

    return 0;
}

Nested for Loop¶

#include <iostream>

int main() {
    // Multiplication table of 2
    for (int i = 1; i <= 9; i++) {
        std::cout << "2 x " << i << " = " << 2 * i << std::endl;
    }

    // Star triangle
    for (int i = 1; i <= 5; i++) {
        for (int j = 1; j <= i; j++) {
            std::cout << "*";
        }
        std::cout << std::endl;
    }

    return 0;
}

Output:

*
**
***
****
*****

Range-based for Loop (C++11)¶

#include <iostream>
#include <vector>

int main() {
    int arr[] = {1, 2, 3, 4, 5};

    // Array traversal
    for (int num : arr) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    // Modification by reference
    for (int& num : arr) {
        num *= 2;
    }

    // Vector traversal
    std::vector<std::string> names = {"Alice", "Bob", "Charlie"};
    for (const auto& name : names) {
        std::cout << name << std::endl;
    }

    return 0;
}

10. while Loop¶

Basic while Loop¶

#include <iostream>

int main() {
    int count = 1;

    while (count <= 5) {
        std::cout << count << " ";
        count++;
    }
    std::cout << std::endl;  // 1 2 3 4 5

    return 0;
}

Infinite Loop and Breaking¶

#include <iostream>

int main() {
    int num;

    while (true) {
        std::cout << "Enter a number (0 to exit): ";
        std::cin >> num;

        if (num == 0) {
            break;  // Exit loop
        }

        std::cout << "Input: " << num << std::endl;
    }

    std::cout << "Exited" << std::endl;

    return 0;
}

11. do-while Loop¶

Executes at least once.

#include <iostream>

int main() {
    int num;

    do {
        std::cout << "Enter a number between 1 and 10: ";
        std::cin >> num;
    } while (num < 1 || num > 10);  // Repeat if condition is true

    std::cout << "You entered: " << num << std::endl;

    return 0;
}

while vs do-while¶

#include <iostream>

int main() {
    int x = 0;

    // while: Condition checked first
    while (x > 0) {
        std::cout << "while executed" << std::endl;
        x--;
    }
    // No output

    // do-while: Executes at least once
    do {
        std::cout << "do-while executed" << std::endl;
        x--;
    } while (x > 0);
    // "do-while executed" is printed

    return 0;
}

12. break and continue¶

break¶

Immediately exits the loop.

#include <iostream>

int main() {
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            break;  // Exit at 5
        }
        std::cout << i << " ";
    }
    std::cout << std::endl;  // 1 2 3 4

    return 0;
}

continue¶

Skips the current iteration.

#include <iostream>

int main() {
    for (int i = 1; i <= 10; i++) {
        if (i % 2 == 0) {
            continue;  // Skip even numbers
        }
        std::cout << i << " ";
    }
    std::cout << std::endl;  // 1 3 5 7 9

    return 0;
}

13. Operator Precedence¶

Precedence	Operators
1 (highest)	`()`, `[]`, `->`, `.`
2	`!`, `~`, `++`, `--`, `sizeof`
3	`*`, `/`, `%`
4	`+`, `-`
5	`<<`, `>>`
6	`<`, `<=`, `>`, `>=`
7	`==`, `!=`
8	`&`
9	`^`
10	`\\|`
11	`&&`
12	`\\|\\|`
13	`?:`
14 (lowest)	`=`, `+=`, `-=`, etc.

Tip: When in doubt, use parentheses!

14. Summary¶

Category	Operators
Arithmetic	`+`, `-`, `*`, `/`, `%`
Comparison	`==`, `!=`, `<`, `>`, `<=`, `>=`
Logical	`&&`, `\\|\\|`, `!`
Bitwise	`&`, `\\|`, `^`, `~`, `<<`, `>>`
Assignment	`=`, `+=`, `-=`, `*=`, `/=`

Control Flow	Purpose
`if-else`	Conditional branching
`switch`	Multiple branching
`for`	Count-based iteration
`while`	Condition-based iteration
`do-while`	Executes at least once

Next Step¶

Let's learn about functions in 04_Functions.md!