Learning how to Read and output Lines in a file in C

The first issue I see is this idiom:

while((c = fgetc(myFile) != EOF))

has the parens wrong, it should be:

while ((c = fgetc(myFile)) != EOF)

Also, this count:

start = line - num; //Start location

has an off-by-one error:

int start = line - num - 1; // Start location

Beyond that, your array seems too small for general text line processing:

char c, array[100];

Putting it all together with a few style tweaks, we get:

// Tail function that prints the lines
// according to the user specified number of lines
void tail(FILE *myFile, int num)
{
    int line = 0;
    char c;
    while ((c = fgetc(myFile)) != EOF)
    {
        if (c == '\n')
        {
            line++;
        }
    }
    int start = line - num - 1; // Start location
    (void) fseek(myFile, 0, SEEK_SET); // Go to the start of the file
    int counter = 0;
    char array[1024];
    while (fgets(array, sizeof(array), myFile) != NULL)
    {
        if (counter > start)
        {
            fputs(array, stdout); // Print the string
        }
        counter++;
    }
    fclose(myFile); // Close the file
}