Pass Inputs and Return Results
Pass Inputs and Return Results
Parameters receive a call’s inputs and return supplies a result to its caller.
A two-subject total makes the direction of data explicit without changing the caller’s marks.
Before this lesson, review Give a Task a Name when needed.
What you’ll learn
- Use parameters and return values to pass Inputs and Return Results.
- Explain how the complete example produces 75.
- Make the practice change and explain why the result changes or stays the same.
Follow a complete C++ example
A two-subject total makes the direction of data explicit without changing the caller’s marks.
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 total(int first, int second) {
return first + second;
}
int main() {
std::cout << total(35, 40) << '\n';
return 0;
}
Expected output
75Connect the code to its result
C++17 · source used in this explanation
#include <iostream>
int total(int first, int second) {
return first + second;
}
int main() {
std::cout << total(35, 40) << '\n';
return 0;
}
Expected output
75Parameters receive a call’s inputs and return supplies a result to its caller. A two-subject total makes the direction of data explicit without changing the caller’s marks.
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 75. In this example, distinguish what the program calculates or changes from what it actually displays.
Important mistakes and boundaries
Ordinary value parameters are copies. A function returning int should return a value on every normal path.
Change the school example
C++17 · edit this complete example
#include <iostream>
int total(int first, int second) {
return first + second;
}
int main() {
std::cout << total(35, 40) << '\n';
return 0;
}
Your task: Use subject marks 40 and 45. 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: Use subject marks 40 and 45. The returned total is 85.
Parameters receive a call’s inputs and return supplies a result to its caller. A two-subject total makes the direction of data explicit without changing the caller’s marks.
Ordinary value parameters are copies. A function returning int should return a value on every normal path.
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 total(int first, int second) {
return first + second;
}
int main() {
std::cout << total(40, 45) << '\n';
return 0;
}
Expected output
85Check your understanding
C++17 · original program for this question
#include <iostream>
int total(int first, int second) {
return first + second;
}
int main() {
std::cout << total(35, 40) << '\n';
return 0;
}
What to remember
Parameters receive a call’s inputs and return supplies a result to its caller. Ordinary value parameters are copies. A function returning int should return a value on every normal path.
Useful connections: 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.