Editing For loop (section)

==Loop counters==
In [[computer programming]], a ''' loop counter''' is a control variable that controls the iterations of a loop (a computer [[programming language]] construct). It is so named because most uses of this construct result in the variable taking on a range of integer values in some orderly sequences (for example., starting at 0 and ending at 10 in increments of 1)

Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate and for the program flow to continue to the next [[instruction (computer science)|instruction]] after the loop.

A common [[identifier naming convention]] is for the loop counter to use the variable names '''i''', '''j''', and '''k''' (and so on if needed), where '''i''' would be the most outer loop, '''j''' the next inner loop, etc. The reverse order is also used by some programmers. This style is generally agreed to have originated from the early programming of Fortran{{Citation needed|date=August 2009}}, where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to [[mathematical notation]] where [[index notation|indices]] for [[summation|sums]] and [[multiplication]]s are often '''i''', '''j''', etc. A variant convention is the use of duplicated letters for the index, '''ii''', '''jj''', and ''' kk''', as this allows easier searching and search-replacing than using a single letter.<ref>http://www.knosof.co.uk/vulnerabilities/loopcntrl.pdf Analysis of loop control variables in C</ref>

===Example===
An example of C code involving nested for loops, where the loop counter variables are '''i''' and '''j''':

<syntaxhighlight lang="c">
for (i = 0; i < 100; i++) {
    for (j = i; j < 10; j++) {
        some_function(i, j);
    }
}
</syntaxhighlight>

Loops in C can also be used to print the reverse of a word. As:
<syntaxhighlight lang="c">
for (i = 0; i < 6; i++) {
    scanf("%c", &a[i]);
}
for (i = 4; i >= 0; i--) {
    printf("%c", a[i]);
}
</syntaxhighlight>
Here, if the input is {{code|apple}}, the output will be {{code|elppa}}.