Control flow with conditions and loops
Branch on conditions and repeat work with familiar control structures.
- Write
ifstatements,forloops, andwhileloops with explicit blocks.
Use if and else to choose a path, and loops to repeat work. C++ conditions use boolean expressions; comparisons such as == produce a bool. A for loop is handy when the update step is clear, while while repeats as long as its condition remains true. Braces make the body explicit and reduce accidental control-flow mistakes.
1#include <iostream>
2
3int main() {
4 for (int n = 1; n <= 3; ++n) {
5 if (n % 2 == 0) {
6 std::cout << n << " is even\n";
7 } else {
8 std::cout << n << " is odd\n";
9 }
10 }
11}1 is odd 2 is even 3 is odd
++n increments before producing its value; for a built-in integer in this loop, n++ would also work. Use == to compare and = to assign. An accidental assignment in a condition can compile and change the program’s behavior.
Key takeaways
Use branches for decisions and loops for repetition.
Keep assignment
=distinct from comparison==.Make loop bounds and termination conditions clear.
Lesson quiz
5 questions · pass with 4 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
Practice: write C++
Write C++20 in the editor and run it against sample input. GCC 14 compiles the code through Compiler Explorer, a free public service; your source and test input are sent there.
Sum from one to n
Read an integer n and print the sum of all integers from 1 through n as Sum: N. Assume n is between 1 and 1000.
- Sum to 5
- Sum to 1
Your code is compiled as C++20 with gcc 14 (-Wall -Wextra) and run on Compiler Explorer (godbolt.org), a free public service.
Questions about this lesson
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