A simple C program to count all the lines in a file

count_lines.c

#include <stdio.h>
#include <stdbool.h>

int main(int argc, char* argv[])
{
    // Check that enough arguments were given
    if(argc != 2)
    {
        fprintf(stderr, "Usage:\n\tcount_lines <filename>\n");
        return 1;
    }

    // Try and open the file
    FILE* fp;
    if (!(fp = fopen(argv[1], "r")))
    {
        fprintf(stderr, "Unable to open file %s\n", argv[1]);
        return 1;
    }

    // Initialise some variables
    const unsigned int buffer_length = 4096;
    char buffer[buffer_length];
    unsigned int num_lines = 0;

    // Loop through the file
    while (true)
    {
        // Get the next line
        fgets(buffer, buffer_length, fp);

        // Check if we reached the end of the file
        if(feof(fp))
            break;

        // Increment the line counter
        num_lines++;
    }

    // Close the file
    fclose(fp);

    // How many lines was that?
    printf("The file %s contains %u lines\n", argv[1], num_lines);

    return 0;
}