Practical C Programming

How to do it…

1. Open the source file in read-only mode using the following code:

fp = fopen (argv [1],"r");

2. If the file does not exist or does not have enough permissions, an error message will be displayed and the program will terminate, as shown in the following code:

if (fp == NULL) {    printf("%s file does not exist\n", argv[1]);    exit(1); }

3. Open the destination file, the file where the encrypted text will be written, in write-only mode using the following code:

fq = fopen (argv[2], "w");

4. Read a line from the file and access each of its characters using the following code:

fgets(buffer, BUFFSIZE, fp);

5. Using the following code, subtract a value of 45 from the ASCII value of each of the characters in the line to encrypt that character: ...