/in/ex1.c: In function 'main':
/in/ex1.c:19:16: error: conversion to 'int' from 'size_t {aka long unsigned int}' may alter its value [-Werror=conversion]
   for (int k = strlen(filename[j]); filename[j][k] == '.'; k--)
                ^~~~~~
cc1: all warnings being treated as errors