# [ACCEPTED]-Who "invented" i,j,k as integer counter variable names?-loop-counter

i = integer

Comes from Fortran where integer 10 variables had to start with the letters 9 I through N and real variables started with 8 the other letters. Thus I was the first 7 and shortest integer variable name. Fortran 6 was one of the earliest programming languages 5 in widespread use and the habits developed 4 by programmers using it carried over to 3 other languages.

(From: Why are we using i as a counter in loops)

Obviously, `j`

and 2 `k`

are just the next ones in your favorite 1 alphabet.

The Mathematicians :)

0

It's common from school-level and college-level 10 algebra exercises (although `x`

and `y`

had their 9 part to play, there, too :-)

Also, if I remember 8 correctly, the early programming languages 7 (like early versions of `FORTRAN`

) used variable 6 naming in a way where initial letters were 5 significant, and this may have had a part 4 to play. For example, as this page says:

A FORTRAN 3 variable is a way of referring to a cell 2 of the computer. Names for variables must 1 conform to the following rules:

- The name may be from one to six characters.
- The first character must be a letter.
- Characters other than the first may be letters or numeric digits.
- If the first character is I, J, K, L, M or N, the variable is integer (i.e. can hold a whole number value). Otherwise, it is real (i.e. can hold a value according to the floating point convention).

FORTRAN. If the first character is I, J, K, L, M 4 or N, the variable is integer (i.e. can 3 hold a whole number value). Otherwise, it 2 is real (i.e. can hold a value according 1 to the floating point convention).

I always thought i stands for index as used 1 eg in sum formulas in mathematics.

From the wikipedia for Loop Counter

A common identifier 14 naming convention is for the loop counter 13 to use the variable names i, j and k (and 12 so on if needed), where i would be the 11 most outer loop, j the next inner loop, etc. The 10 reverse order is also used by some programmers. This 9 style is generally agreed to have originated from 8 the early programming of FORTRAN, where 7 these variable names beginning with these 6 letters were implicitly declared as having 5 an integer type, and so were obvious choices 4 for loop counters that were only temporarily required. The 3 practice also dates back further to mathematical 2 notation where indices for sums and multiplications are 1 often i, j, etc.

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