C Compile and run

Lesson notes

Compile and run

Learn to compile and run a C program with gcc.

Compiling with gcc

To run a C program you first need to compile it. The most common compiler is gcc. To compile hello.c into an executable named hello:

gcc hello.c -o hello

Then run it with ./hello. The -o hello part sets the output file name; without it the default name is a.out.

Compilation stages

Compilation actually has four stages:

Preprocessing: #include and #define are expanded
Compilation: code is turned into assembly
Assembly: assembly is turned into machine code
Linking: external libraries are added

gcc runs all stages with a single command.

Test yourself

Which command produces an executable?
- execute hello.c
- run hello.c
- gcc hello.c -o hello
- compile hello.c
Show answer

gcc hello.c -o hello — gcc hello.c -o hello compiles hello.c into an executable named hello.

Output file flag

gcc hello.c ____ hello

Show answer

gcc hello.c -o hello

Match the commands

gcc

Compiler
./hello

Run
hello.c

Source file
a.out

Default output
What is produced by 'gcc main.c'?
- main.exe
- program
- main.class
- a.out
Show answer

a.out — Without -o, gcc names the output a.out.

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