Oh, didn't know that about the calloc, thank you for pointing this out!

ok, looking on others people solutions I think I'm dumb

When building C code compiler returns this mistake:
fixture.c: 16: 20: warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]
for (int i = 0; i <input_sz; i ++)
~ ^ ~~~~~~~~
Can be easily fixed either by adding 'unsigned' into the for loop or by deleting unsinged from input_sz variable.