properly add header and file opening

.gitignore

@@ -0,0 +1 @@
+a.out

testconvert.c

@@ -11,11 +11,17 @@ typedef struct {
 	uint32_t zeroed;
 	uint16_t zeroed_2;
 } bmp_header;
-struct bmp_header input_hdr;
+bmp_header input_hdr;
 int main(int argc, char** argv) {
 	if (argc != 2) {
-		printf("usage: %s <filename>", argv[0]);
+		printf("usage: %s <filename>\n", argv[0]);
+		return 1;
 	}
 	const char* filename = argv[1];
-	printf("%s", filename);
+	printf("%s\n", filename);
+	FILE* working_file = fopen(filename, "r");
+	if (!working_file) {
+		printf("error opening file\n");
+		return 1;
+	}
 }