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Order and Find Records

Order and Find Records

Standard algorithms express common range operations.

Sort changes the sequence’s order; find locates a matching element and returns end when no match exists.

Before this lesson, review Represent a Position in a Range when needed.

What you’ll learn

  • Use sorting and searching to order and Find Records.
  • Explain how the complete example produces 70 → true.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

Sort changes the sequence’s order; find locates a matching element and returns end when no match exists.

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>
#include <vector>
#include <algorithm>

int main()  {
  std::vector<int> marks {
    80, 70, 90
  }
  ;
  std::sort(marks.begin(), marks.end());
  auto found = std::find(marks.begin(), marks.end(), 80);
  std::cout << marks.front() << '\n' << std::boolalpha << (found != marks.end()) << '\n';
  return 0;
}

Expected output

70
true
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>
#include <vector>
#include <algorithm>

int main()  {
  std::vector<int> marks {
    80, 70, 90
  }
  ;
  std::sort(marks.begin(), marks.end());
  auto found = std::find(marks.begin(), marks.end(), 80);
  std::cout << marks.front() << '\n' << std::boolalpha << (found != marks.end()) << '\n';
  return 0;
}

Expected output

70
true

Standard algorithms express common range operations. Sort changes the sequence’s order; find locates a matching element and returns end when no match exists.

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 70 → true. In this example, distinguish what the program calculates or changes from what it actually displays.

Important mistakes and boundaries

Binary search requires a range sorted according to its comparison. Find is a linear search and does not require prior sorting.

Change the school example

C++17 · edit this complete example

#include <iostream>
#include <vector>
#include <algorithm>

int main()  {
  std::vector<int> marks {
    80, 70, 90
  }
  ;
  std::sort(marks.begin(), marks.end());
  auto found = std::find(marks.begin(), marks.end(), 80);
  std::cout << marks.front() << '\n' << std::boolalpha << (found != marks.end()) << '\n';
  return 0;
}

Your task: Search for 85 instead. 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: Search for 85 instead. The first mark remains 70 and the match result becomes false.

Standard algorithms express common range operations. Sort changes the sequence’s order; find locates a matching element and returns end when no match exists.

Binary search requires a range sorted according to its comparison. Find is a linear search and does not require prior sorting.

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>
#include <vector>
#include <algorithm>

int main()  {
  std::vector<int> marks {
    80, 70, 90
  }
  ;
  std::sort(marks.begin(), marks.end());
  auto found = std::find(marks.begin(), marks.end(), 85);
  std::cout << marks.front() << '\n' << std::boolalpha << (found != marks.end()) << '\n';
  return 0;
}

Expected output

70
false
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>
#include <vector>
#include <algorithm>

int main()  {
  std::vector<int> marks {
    80, 70, 90
  }
  ;
  std::sort(marks.begin(), marks.end());
  auto found = std::find(marks.begin(), marks.end(), 80);
  std::cout << marks.front() << '\n' << std::boolalpha << (found != marks.end()) << '\n';
  return 0;
}
Before making the practice edit, what does the original C++17 program print?
Choose one answer. You can try again.

Answer and explanation

70 true

Standard algorithms express common range operations. Sort changes the sequence’s order; find locates a matching element and returns end when no match exists. Binary search requires a range sorted according to its comparison. Find is a linear search and does not require prior sorting.

What to remember

Standard algorithms express common range operations. Binary search requires a range sorted according to its comparison. Find is a linear search and does not require prior sorting.

Useful connections: Represent a Position in a Range, 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.

    Next lesson: Pass a Small Operation →