Appending to a text file

[Aia]

I'm at the point of learning how to write to a file. I created these lines as a test.
My concern is that it doesn't look right that I have to write the same sentences for displaying it to screen and to put it in file.

/*
 * data.c
 * test opening and appending to
 * a file.
 */

#include <stdio.h>

int read_int(int *result);
char *read_string(char *string, int size);

int main(void)
{
    int n1, n2;
    char name[20];
    FILE *file_ptr;

     file_ptr = fopen("data.txt", "a");
    if(!file_ptr)
    {
        printf("Error opening file");
        return(1);
    }
    else
    {
        fprintf(file_ptr,"What's your name?: ");
        fprintf(stdout,"What's your name?: ");
        read_string(name, sizeof name / sizeof *name);
        fprintf(file_ptr,"%s\n", name);
    }
    printf("Enter value for first number: ");
    fflush(stdout);
    read_int(&n1);
    printf("Enter value for second number: ");
    fflush(stdout);
    read_int(&n2);
    
    fprintf(file_ptr,"n1 = %d\nn2 = %d\n", n1, n2);
    fclose(file_ptr);
    
    system("PAUSE");

    return(0);
}

int read_int(int *result)
{
        char ch, buffer[13];
        return fgets(buffer, sizeof buffer, stdin) && !isspace(*buffer) &&
        sscanf(buffer, "%d%c", result, &ch) == 2 && (ch == '\0' || ch == '\n');
}

char *read_string(char *string, int size)
{
    if(fgets(string, size, stdin) != NULL)
    {
        int len = strlen(string)-1;
        if(string[len] == '\n')
       {
           string[len] = '\0';
        }
        else 
        {
            int ch;
            do
            {
                ch = getchar();
            }
            while(ch != '\n' && ch != EOF);
        }
    }
    return string;
}

fprintf(file_ptr,"What's your name?: ");
fprintf(stdout,"What's your name?: ");

Is there another better way of doing this so I don't have to repeat so much code every time?.

[John A]

You asked this question already.

What you should do is create a function that does the screen and file printing; all you have to do is pass the string and the file as arguments.

I was thinking something like this:

void printToFileAndScreen(FILE *filePtr, char *myString) {

    if (myString) {
        fprintf(stdout, myString);
        fprintf(filePtr, myString);
    }
}

Note that this fprintf() wrapper is not nearly as robust as the fprintf() function; it certainly doesn't accept any extra parameters. However, this should help to reduce the bulk of your code by a bit.

Additionally, do not forgot to flush the streams, either in this function, or in the main() function like you were already doing.

[Aia]

Yes, I asked a question related to this topic, and this piece of code is the result of what I understood from you and some more reading.
Sorry, I didn't want to bother you. I didn't want you to write me a function, I just wanted confirmation that what I was understanding is correct code.

[John A]

Sorry, I didn't want to bother you. I didn't want you to write me a function, I just wanted confirmation that what I was understanding is correct code.

That's OK. ;)

Anyway, you have to keep several things in mind with C/C++: Don't assume anything. If it doesn't look like it's going to do something, don't assume it does. An example of this is memory management. Well, actually C takes care of any statically allocated variables, but as soon as you start using dynamic memory... you're on your own!

What does this mean for you? It usually means that there's no easy prewritten function for any semi-complex task you want to accomplish. Most often you have to implement it yourself, as is the case here.