Indexing does that, but the indices must vary in a certain range, whose limits are frequently determined by using something like "sizeof(array)/sizeof(element)" which is an unsigned number.
This is especially inconvenient in C, where there exist extremely dangerous legacy implicit casts between signed integers and unsigned integers, which have a great probability of generating incorrect values.
Because the index is typically a signed integer, comparing it with an unsigned limit without using explicit casts is likely to cause bugs. Using explicit casts of smaller unsigned integers towards bigger signed integers results in correct code, but it is cumbersome.
These problems are avoided as said in TFA, by making "sizeof" and the like to have 64-bit signed integer values, instead of unsigned values.
Well chosen implicit conversions are good for a programming language, by reducing unnecessary verbosity, but the implicit integer conversions of C are just wrong and they are by far the worst mistake of C much worse than any other C feature.
Other C features are criticized because they may be misused by inexperienced or careless programmers, but most of the implicit integer conversions are just incorrect. There is no way of using them correctly. Only the conversions from a smaller signed integer to a bigger signed integer are correct.
Mixed signedness conversions have always been wrong and the conversions between unsigned integers have been made wrong by the change in the C standard that has decided that the unsigned integers are integer residues modulo 2^N and they are not non-negative integers.
For modular integers, the only correct conversions are from bigger numbers to smaller numbers, i.e. the opposite of the implicit conversions of C. The implicit conversions of C unsigned numbers would have been correct for non-negative integers, but in the current C standard there are no such numbers.
The current C standard is inconsistent, because the meaning of sizeof is of a non-negative integer and this is also true for the conversions between unsigned numbers, but all the arithmetic operations with unsigned numbers are defined to be operations with integer residues, not operations with non-negative numbers.
The hardware of most processors implements at least 3 kinds of arithmetic operations: operations with signed integers, operations with non-negative integers and operations with integer residues.
Any decent programming language should define distinct types for these kinds of numbers, otherwise the only way to use completely the processor hardware is to use assembly language. Because C does not do this, you have to use at least inline assembly, if not separate assembly source files, for implementing operations with big numbers.