Read from file in C and execute conditional logic - c

Question

I am new to programming and have a few questions as to how to implement this idea.
I am looking to have a user enter their name/string of digits and if their name is on a list, to then execute a string of commands. I am not to sure how to impliment this, but with some gogle-ing I was able to come up with this code:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char userName[10];
printf("\n\n\n\nPlease enter your name: ");
scanf_s("%s",userName); // userName should be verified/found inside the results.dat file
FILE *fp;
fp = fopen("results.dat", "r");
if (fp == NULL) {
printf("I couldn't open results.dat for writing.\n");
exit(0);
}
if (fp == John) {
//Dispence squence of pills for John
}
if (fp == Mary) {
//Dispence squence of pills for Mary
}
return 0;
}
I do not think I am using the if statement correctly. how can I do something like:
if (content in fp == john, execute/call another function)
Thanks in advance!

Answer 1

Try this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char userName[10];
char names[20];
printf("\n\n\n\nPlease enter your name: ");
scanf("%s",userName); // userName should be verified/found inside the results.dat file
FILE *fp;
fp = fopen("results.dat", "r");
if (fp == NULL) {
printf("I couldn't open results.dat for writing.\n");
exit(0);
}
while(fgets(names, 20, fp)) // fgets reads a line from the file
{
names[strlen(names)-1] = '\0'; // but it leaves the newline character "\n" , so the strings won't match
if(strcmp(names, userName) == 0) // if the value returned by strcmp is zero then string match
{
printf("Match found\n");
}
}
return 0;
}

Answer 2

fopen simply opens a file for reading and/or writing, to read the actual content of the file you need to use functions such as fgets, fscanf and so on.
Short example
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char* argv[])
{
char name[64];
char buffer[64];
printf ("Please enter your name: ");
file = fopen ("results.dat", "rw");
if (!file) {
printf ("Results.dat could not be opened.\n");
exit(-1);
}
if ( fgets (buffer, 64, file)) {
if (strcmp (buffer, "john")) {
printf ("Contents of file is john\n");
}
}
return 0;
}