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Error: Unterminated comment (Invalid comment block) in C | Common C program Errors

Here, we will learn how and when "Unterminated comment" error occurs (Invalid comment block) in C and how to fix it?
By IncludeHelp Last updated : March 10, 2024

Comments are used to write logic explain or anything that you do not want to compile. In C language there are two types of comments 1) Single line comment and 2) Multi-line comment.

Read: Comments in C language

Error: Unterminated comment (Invalid comment block)

Unterminated comment error occurred when we do not terminate the comment with a valid set of characters.

Single line comment does not need to terminate, and it starts by a double slash (//), but, multiple line comment needs to be terminated by */ (asterisk and slash).

Consider the program:

Example

#include <stdio.h>

int main(void) {

    /*printf is used to print a message \*
    printf("Hello world");
    
    return 0;
}

Output

prog.c: In function ‘main’:
prog.c:5:5: error: unterminated comment
     /*printf is used to print a message \*
     ^
prog.c:3:1: error: expected declaration or statement at end of input
 int main(void) {
 ^~~

How to fix Unterminated comment error in C

Note that, multiple line comment are placed between /* and */, terminate the comment properly with valid characters.

Correct Code

#include <stdio.h>

int main(void) {

    /*printf is used to print a message*/
    printf("Hello world");
    
    return 0;
}

Output

Hello world

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