Consider the program:

#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