Repeat a Known Range
Repeat a Known Range
A for loop groups initialization, continuation and update.
Printing three roll numbers demonstrates exactly which values the loop reaches.
Before this lesson, review Choose a Short Value when needed.
What you’ll learn
- Use for loop to repeat a Known Range.
- Explain how the complete example produces 1 → 2 → 3.
- Make the practice change and explain why the result changes or stays the same.
Follow a complete C++ example
Printing three roll numbers demonstrates exactly which values the loop reaches.
Read the declarations above main before tracing its statements. Each declared name supplies the value, type or operation used later. The std:: prefix selects a name from the standard library, and cout << sends a value to the output stream.
C++17 · main.cpp · complete program
#include <iostream>
int main() {
for (int roll = 1; roll <= 3; ++roll) {
std::cout << roll << '\n';
}
return 0;
}
Expected output
1
2
3Connect the code to its result
C++17 · source used in this explanation
#include <iostream>
int main() {
for (int roll = 1; roll <= 3; ++roll) {
std::cout << roll << '\n';
}
return 0;
}
Expected output
1
2
3A for loop groups initialization, continuation and update. Printing three roll numbers demonstrates exactly which values the loop reaches.
Trace the result: Read the complete program below from its starting values to the output operations. Each std::cout statement displays the value supplied at that point; \n begins the next line. The resulting lines, in order, are 1 → 2 → 3. In this example, distinguish what the program calculates or changes from what it actually displays.
Repeat a Known Range: cause and effect
Operation
A for loop groups initialization, continuation and update.
Effect on school data
Printing three roll numbers demonstrates exactly which values the loop reaches.
Observed result
The program displays these lines after the shown operations.
1 2 3
Important mistakes and boundaries
The condition runs before each iteration. A bound of roll < 3 would exclude roll number 3.
Change the school example
C++17 · edit this complete example
#include <iostream>
int main() {
for (int roll = 1; roll <= 3; ++roll) {
std::cout << roll << '\n';
}
return 0;
}
Your task: Change the upper bound to 2. Before running your edited program, predict the new output and explain which stored value, condition or object changes. Keep the rest of the example intact.
Use the complete source repeated here; this task does not depend on remembering code from another section.
Worked answer and reasoning
Worked variation: Change the upper bound to 2. Only 1 and 2 print.
A for loop groups initialization, continuation and update. Printing three roll numbers demonstrates exactly which values the loop reaches.
The condition runs before each iteration. A bound of roll < 3 would exclude roll number 3.
For a baseline run, save this source as main.cpp and use clang++ -std=c++17 -Wall -Wextra -pedantic main.cpp -o school, or equivalent g++ flags. Recompile after editing so that you run the updated executable.
The source and output below belong to the edited program. Compare them with the original example to see the consequence of this single change.
C++17 · worked variation · complete program
#include <iostream>
int main() {
for (int roll = 1; roll <= 2; ++roll) {
std::cout << roll << '\n';
}
return 0;
}
Expected output
1
2Check your understanding
C++17 · original program for this question
#include <iostream>
int main() {
for (int roll = 1; roll <= 3; ++roll) {
std::cout << roll << '\n';
}
return 0;
}
What to remember
A for loop groups initialization, continuation and update. The condition runs before each iteration. A bound of roll < 3 would exclude roll number 3.
Useful connections: Choose a Short Value, Give a Task a Name.
Language and design guidance: C++ Core Guidelines and C++ working draft. The draft describes an evolving language; these examples deliberately target C++17.
Reaching the recap and completing the quizzes are separate milestones.