What is an ideal variable naming convention for loop variables?

My experience is that most people use single letters, e.g.: i, j, k, ... or x, y, or r, c (for row/column) or w, h (for width/height) , etc.

But I learned a great alternative a long time ago, and have used it ever since: double letter variables.

// recommended style              ●    // "typical" single-letter style
                                  ●
for (ii=0; ii<10; ++ii) {         ●    for (i=0; i<10; ++i) {
    for (jj=0; jj<10; ++jj) {     ●        for (j=0; j<10; ++j) {
        mm[ii][jj] = ii * jj;     ●             m[i][j] = i * j;
    }                             ●        }
}                                 ●    }

In case the benefit isn't immediately obvious: searching through code for any single letter will find many things that aren't what you're looking for. The letter i occurs quite often in code where it isn't the variable you're looking for.

@JustMike . . . A FEW C EXAMPLES: . . . to accompany the Java ones.

NON-NESTED loop: . . . limiting scope where possible

/*LOOP_DESCRIPTION*/ {

    int i;

    for (i = 0; i < LOOP_LENGTH; i++) {

        // loop body
    }  
}

NESTED loop: . . . ditto

/*LOOP_DESCRIPTION*/ {

    int row, column;

    for (row = 0; row < ROWS; row++) {

        for (column = 0; column < COLUMNS; column++) {

            // loop body
        }
    }  
}

One good thing about this layout is it reads badly without comments, thereby encouraging them.
It's verbose perhaps, but personally this is how I do loops in C.

Also: I did use "index" and "idx" when I started, but this usually got changed to "i" by my peers.

for numerical computations, matlab, and the likes of it, dont use i, j

these are reserved constants, but matlab wont complain.

My personal favs are

index first,second counter count