Compilation and execution process in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the first step in the C++ compilation process?

The first step is preprocessing, where directives like #include and #define are handled.

beginner

What does the compiler do after preprocessing?

After preprocessing, the compiler translates the code into assembly language or object code.

intermediate

What is the role of the linker in the compilation process?

The linker combines object files and libraries to create the final executable program.

beginner

Explain what happens during the execution phase of a C++ program.

During execution, the operating system loads the executable into memory and runs the program instructions step by step.

beginner

Why is compilation important before running a C++ program?

Compilation translates human-readable code into machine code that the computer can understand and execute.

Which step comes immediately after preprocessing in C++ compilation?

A Loading

B Linking

C Execution

D Compilation

After preprocessing, the compiler translates the code into object code during the compilation step.

What does the linker do?

A Combines object files into an executable

B Preprocesses directives

C Runs the program

D Converts source code to machine code

The linker combines object files and libraries to create the final executable.

Which of these is NOT part of the compilation process?

A Preprocessing

B Execution

C Linking

D Compilation

Execution happens after compilation and linking, when the program runs.

What is the output of the compilation step?

A Object code

B Executable file

C Source code

D Preprocessed code

Compilation produces object code, which is then linked to form an executable.

Who loads the executable into memory to run it?

A Compiler

B Linker

C Operating system

D Preprocessor

The operating system loads the executable into memory and starts execution.

Describe the main steps involved in turning C++ source code into a running program.

Think about what happens from writing code to seeing it run.

Explain why the linker is necessary in the compilation and execution process.

Consider what happens when your program uses multiple files or libraries.

Practice

1. What is the main purpose of the compilation step in C++ programming?

easy

A. To convert human-readable code into machine code

B. To run the program and show output

C. To write the source code

D. To debug the program automatically

Solution

1. Step 1: Understand what compilation means

   Compilation changes the C++ source code into machine code that the computer can understand.

2. Step 2: Differentiate compilation from execution

   Execution runs the compiled machine code, but compilation itself only converts code.

3. Final Answer:

   To convert human-readable code into machine code -> Option A

4. Quick Check:

   Compilation = convert code [OK]

Hint: Compilation means converting code, not running it [OK]

Common Mistakes:

• Confusing compilation with execution
• Thinking compilation runs the program
• Believing compilation writes code

2. Which of the following is the correct command to compile a C++ file named main.cpp using g++?

easy

A. compile main.cpp

B. run main.cpp

C. g++ main.cpp -o main

D. execute main.cpp

Solution

1. Step 1: Recall the g++ compile command syntax

   The g++ compiler uses the command g++ filename.cpp -o outputname to compile.

2. Step 2: Match the command to the options

   g++ main.cpp -o main matches the correct syntax to compile main.cpp into an executable named main.

3. Final Answer:

   g++ main.cpp -o main -> Option C

4. Quick Check:

   g++ compile command = g++ main.cpp -o main [OK]

Hint: Use g++ filename.cpp -o outputname to compile [OK]

Common Mistakes:

• Using 'run' or 'execute' instead of g++
• Omitting the -o option
• Confusing compile and execute commands

3. Consider this C++ program:

#include <iostream>
int main() {
  std::cout << "Hello" << std::endl;
  return 0;
}

What will happen if you try to execute this program without compiling it first?

medium

A. The program will print "Hello"

B. You will get an error saying the program is not found

C. The program will compile automatically and then run

D. The program will run but show no output

Solution

1. Step 1: Understand execution requires compiled program

   Execution runs the compiled machine code. Without compiling, no executable exists.

2. Step 2: Predict what happens if you run without compiling

   Trying to run without compiling causes an error because the executable file is missing.

3. Final Answer:

   You will get an error saying the program is not found -> Option B

4. Quick Check:

   Execution needs compiled file = error if missing [OK]

Hint: You must compile before running, or get error [OK]

Common Mistakes:

• Assuming execution auto-compiles
• Expecting output without compiling
• Thinking program runs but shows no output

4. You wrote this code in test.cpp:

#include <iostream>
int main() {
  std::cout << "Hi" << std::endl
  return 0;
}

When compiling, you get an error. What is the problem?

medium

A. Wrong return type for main

B. Missing #include <string>

C. Using std::cout incorrectly

D. Missing semicolon after std::endl

Solution

1. Step 1: Check syntax line by line

   The line with std::cout << "Hi" << std::endl is missing a semicolon at the end.

2. Step 2: Identify compilation error cause

   Missing semicolon causes a syntax error during compilation, stopping the process.

3. Final Answer:

   Missing semicolon after std::endl -> Option D

4. Quick Check:

   Semicolon missing = syntax error [OK]

Hint: Check for missing semicolons after statements [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking #include <string> is needed here
• Assuming return type is wrong

5. You have two C++ files: main.cpp and helper.cpp. You want to compile both and run the program. Which command correctly compiles and links both files into one executable named app?

hard

A. g++ main.cpp helper.cpp -o app

B. g++ main.cpp -o app helper.cpp

C. g++ -o app main.cpp; g++ helper.cpp

D. compile main.cpp helper.cpp app

Solution

1. Step 1: Understand compiling multiple files

   To compile multiple source files together, list them all in one g++ command.

2. Step 2: Check command syntax for linking

   g++ main.cpp helper.cpp -o app correctly lists both files and uses -o to name the executable.

3. Final Answer:

   g++ main.cpp helper.cpp -o app -> Option A

4. Quick Check:

   Multiple files compile = list all in one g++ command [OK]

Hint: List all source files in one g++ command to compile [OK]

Common Mistakes:

• Trying to compile files separately without linking
• Wrong order or syntax in command
• Using unknown 'compile' command