My self written cat implementation

cat.c

#include <stdint.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
	int file_index = 0; // index of the current file
	while (file_index + 1 < argc || file_index == 0) {
		FILE *file; // contains the pointer to the file
		if (file_index + 1 == argc) { // no file path is given, use stdin
			file = stdin;
		} else { // file path is given, argv[file_index + 1] is file path
			file = fopen(argv[file_index + 1], "r");
			if (file == NULL) { // check for an error
				perror("error while reading file");
				return 1;
			}
		}

		// iterate over bytes
		while (1) {
			uint8_t buf[256]; // read in 256 byte steps
			int size = fread(buf, sizeof(uint8_t), 256, file);
			if (size < 0) {
				perror("error while reading from file");
				return 1;
			}
			if (fwrite(buf, sizeof(uint8_t), size, stdout) < 0) {
				perror("error while writing to stdout");
				return 1;
			}
			if (size < 256) { // file reached the end
				break;
			}
		}

		file_index++;
	}
	return 0;
}