#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define INFILE "questions.txt"
 
 
int main(int argc, char *argv[]) {
        char mc;
        char rt;
        char filename[80];
        char line[255];
 FILE *fin,*fout,*fid;
fin = fopen(INFILE, "r");  
 
 
printf("enter student ID:");   
fgets(line, 255, stdin);
sprintf(filename,"%s.txt",line);
 
fout = fopen(filename, "w");
return 0;
}

printf("enter student ID:");
fgets(line, 255, stdin);
// truncate '\n'
if( line[strlen(line)-1] == '\n')
   line[strlen(line)-1] = '\0';
sprintf(filename,"%s.txt",line);

#include <stdio.h>
#include <string.h>
#define MAXINPUT 100
 
/* Function used if the user didn't pass program parameter */
void getUserInput(void);
 
/* udtf (user defined text filename) is the global character variable buffer.                                                                                   */
char udtf[MAXINPUT];
 
/* Create a constant character array holding the file extentions - you can change the saved file type simply by changing this initialization                                                                               */
const char fext[] = "txt";
 
/* See below for information regarding the keywords "static" and "inline". This is just a header printed for standard information to the user about the program, including how view usage information
or they'll probably never know how.                                                               */
static inline void _header(void)
{
    puts("UDTF (User Define Text Filename) version 1.0");
    printf("Passed parameters or a prompt will allow a user to create a text file whose \nfilename is specifed by the user using the sprintf function");
    printf("For usage \ninformation pass the -h parameter to the program.\n\n");
}
 
/* This is a static funciton which simply means that only the scope of this program is able to access it. Inline means that the function is expanded where it is called; Note that it is not good practice to use inline functions that contain a massive block of code. This function is for usage information at the users request.                                                       */
static inline void _usage(const char *prog_name)
{
    printf("%s -h Show usage help information\n", prog_name);
    printf("%s filename", prog_name);
}
 
int main(int argc, char *argv[])
{
    /* For the noobs sake, the FILE pointer fp will hold a handle or the address returned after issuing the fopen(...) function and will be used for referrence to the open file - which in this case will just close because you simply specified the user create a text file.      */
    FILE *fp;
 
    /* Show program header - refer above for an explaination */
    _header(); 
 
    /* Check to see if the user passed any program parameters so we can use it instead of prompting  the user for a name. Essentially, the argc variable holds the number of parameters passed to the program including the program name itself, which is why its argc > 1 rather than argc > 0.    */
    if (argc > 1)
    {
 
        /* Check if the user requests usage information */
        if (!strcmp(argv[1], "-h"))
        {
 
            /* The program name is pointed to by argv[0] - the first element of the array */
            _usage(argv[0]);
            goto End;
        }
 
        /* So if the user passed a program paremeter which'll represent the name of the text file so we don't have to prompt the user, we first make sure the string length of the first parameter char array pointed to by argv[1] doesn't exceed the MAXINPUT constant defined above.
You can change the max input simply by changing the value assigned to the MAXINPUT constant (i.e #define MAXINPUT 80)                                                                   */
 
        if (strlen(argv[1]) > MAXINPUT) {
 
            /* If the string legnth exceeds MAXINPUT prompt the user */
            getUserInput();
        }
        else
 
            /* Copy the string pointed to by argv[1] into the udtf buffer */
            strcpy(udtf, argv[1]);
    }
    else
        /* If no parameters were passed prompt the user */
        getUserInput();
 
   sprintf(udtf, "%s.%s", udtf, fext);
   /* Attempt to open file use the filename now stored in the udtf buffer and show error if unsuccessful.                                                                         */
    if ((fp = fopen(udtf, "r+")) == NULL) {
        printf("Error: unable to open file %s", udtf);
        return 1;
    }
 
    fclose(fp); /* Close the file */
 
    /* You really shouldn't use goto's they're gay but what-the-hell */
    End:
 return 0;
}
 
/* This function will be used to prompt the user and get the file name via stdin */
void getUserInput(void)
{
    char cinc;
    int a = 0;
 
    printf("Filename: ");
 
    /* While loop getting character by character off stdin using the increment counter a into the global udtf buffer. If you're not aware of what a global variable is, it is a variable that is accessible to all code within the scope of that program. If when the enter key is pressed
or a == MAXINPUT then we want to break the loop and move on.                              */
    while ((cinc = getc(stdin)) != '\n')
    {
        if (a == MAXINPUT)
            break;
        udtf[a] = cinc;
        a++;
    }
 
    /* Before we return add a end-of-string character so we don't print out garabage. */
    udtf[a]= '\0';
}