Often, one line of design is expressed as 5-10 lines of code.

Put the design pseudo-code as a comment.

Example:

/* find largest element in array */
largest = a[0];
for (i = 1; i < N; ++i) {
    if (a[i] > largest)
        largest = a[i];
}

Note: don't put comments that simply echo the code, e.g.

++nlines; /* add one to nlines */