if, else, and Comparisons

Control flow is where a program stops being a calculator and starts making decisions. Input validation, game logic, and the edge-case handling that separates an accepted DSA solution from a rejected one are all ifs and loops arranged carefully. C++'s versions look almost identical to Python's, so this unit is mostly about the few traps where they differ.

if / else if / else

Same idea as Python, different clothing: the condition goes in parentheses, the body goes in braces, and there is no elif, just else if.

int score = 87;

if (score >= 90) {
    std::cout << "A\n";
} else if (score >= 80) {
    std::cout << "B\n";
} else {
    std::cout << "C or below\n";
}

Comparisons: == != < <= > >=. Logic: && is Python's and, || is or, ! is not.

Two classic traps:

• = assigns, == compares. if (x = 5) assigns 5 to x and is always true. Most compilers warn, always read the warning.
• Braces are optional for a single statement, but skipping them causes real bugs when a second line is added later. Always write the braces.