C Comments
Comments in C
Comments are notes for humans. They help explain code and make it easier to read.
They can also be used to temporarily "disable" code while testing.
Comments can be single-line or multi-line.
Remember: Comments are ignored by the compiler, so they do not affect your program's output.
Single-line Comments
Single-line comments start with two forward slashes (//).
Any text between // and the end of the line is ignored by the compiler.
This example uses a single-line comment before a line of code:
This example uses a single-line comment at the end of a line of code:
You can also use // to disable a single line of code:
Multi-line Comments
Multi-line comments start with /* and end with */.
Any text between /* and */ will be ignored by the compiler:
Example
/* The code below will print the words Hello World!
to the screen, and it is
amazing */
printf("Hello World!");
Try it Yourself »
Single or multi-line comments?
It is up to you which you want to use. Normally, we use // for short comments and /* */ for longer comments.
Good to know: Before C99 (released in 1999), you could only use multi-line comments in C.
What the Compiler Sees
Comments are for people reading your code, not for the computer. They help explain what your program does, but they don't affect how it runs.
When you compile your program, comments are ignored.
Here is a program with some helpful comments. Switch the view to see the code without them:
Code
Explanation