http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter3.html
Thus in a for statement, it is possible to
place multiple expressions in the various parts, for example to process two
indices in parallel. This is illustrated in the function reverse(s) ,
which reverses the string s in place. #include < string.h > /* reverse: reverse string s in place */
void reverse(char s[])
{
int c, i, j;
for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
c = s[i];
s[i] = s[j];
...