read unknown integers from text file

i have made a small encyption program nothing fancy really. it turns the letters into 6-9 digit long number seperating each with a \n

i now need to read in each numbers so i can reverse the calculation for the decyrpt but cant seem to work out how to read the number from the text file "output.txt" and store ir as an int so i can preform calculation on it.

i need to do this in c NOT C++ AND NOT C#

if anyone can help id really appriciate it. i tryed using fgetc and concatonating the chars togethers and atio them but coudnt get it to work.

try the code below

Code:

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#include<stdio.h>
#include<stdlib.h>

int
main(){
       
        FILE* fin = fopen("d:\\a.txt","r");
        long ld = 0;
       
        while(fscanf(fin,"%ld\n",&ld) == 1)
                printf("%ld\n",ld);
       
        return EXIT_SUCCESS;
        }

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At some point, aren't you going to be hexed by the encryption program giving you "numbers" that are preceded by zero's, like: "003569"?

How are you going to handle it in your program?