Compiling vs Running

Compiling and running are two distinct steps in getting your program to work. Let's break this down:

Compiling

Compiling is like translating your C++ code into a language your computer understands:

1// Your C++ code (human-readable)
2#include <iostream>
3using namespace std;
4
5int main() {
6  cout << "Hello World!";
7}

The compiler converts this into machine code (not human-readable):

101001000 01100101 01101100 01101100 ...

Running

Running means actually executing the compiled program. Your computer:

1. Loads the machine code into memory
2. Follows the instructions
3. Produces the output

The Complete Process

1. Writing (You create .cpp files)
2. Compiling (Compiler creates .exe or similar)
3. Running (Computer executes the program)

Here's what can happen at each stage:

Compile-Time Errors

The following program is not valid C++. We forgot to include the semicolon, so the compiler cannot understand the code we wrote:

1#include <iostream>
2using namespace std;
3
4int main() {
5  // won't compile!
6  cout << "Forgot semicolon"
7}

1error C2143: syntax error: missing ';' before '}'

Run-Time Errors

The following program has valid code so will compile successfully. However, the code includes an instruction to divide by zero, which will cause an error once we run the program:

1#include <iostream>
2using namespace std;
3
4int main() {
5  // compiles but crashes when run!
6  cout << 100 / 0;
7}

Successful Program

The following program will both compile and run successfully:

1#include <iostream>
2using namespace std;
3
4int main() {
5  // compiles and runs fine
6  cout << "This works!"; 
7}

1This works!

Think of it like baking:

• Writing code is like writing a recipe
• Compiling is like gathering and preparing ingredients
• Running is like actually cooking the dish

You must successfully compile before you can run - just like you need ingredients before you can cook!