| Each function definition can only have one loop. |
It must be possible to do a loop's body more than once [10 points each, 3% max]
| Do not use while to mean if. If you write a loop, there should exist some circumstances where the loop body can be done more than once. |
| A function that contains a loop must not also use recursion. |
Do not emulate two nested loops or two consecutive loops using a single loop. [40 points each, 7% max]
It is possible to do a lot in a single loop by managing variables in
complicated ways. Imagine that you want to do two nested for-loops,
as follows.
for(int i = 0; i < n; i++)
{
for(int j = 0; j < m; j++)
{
doSomething(i,j);
}
}
But that uses two loops, so you emulate it with one loop, as follows.
int i = 0;
int j = 0;
while(i < n)
{
doSomething(i,j);
j++;
if(j == m)
{
j = 0;
i++;
}
}
You can recognize this by the reset of j to 0 when
j = m.
That is not an acceptable way to avoid two loops in one function. Just write a function to handle the inner loop.
void doAll(int i)
{
for(int j = 0; j < m; j++)
{
doSomething(i,j);
}
}
Now your loop becomes
for(int i = 0; i < n; i++)
{
doAll(i);
}
|
The body of a loop must not be a semicolon [4 points each, 2% max]
Never write
while(condition);Do not use a bare semicolon as the body of any type of loop. |
Code that is done at the end of the loop should be written after the loop. [4 points each, 2% max]
Look at the following example.
int loopdemo(int n)
{
for(int i = 0; i < n; i++)
{
doSomething(i);
if(i == n-1)
{
finish(i+1);
}
}
}
Notice that statement finish(i+1) is only done at the end of the
last iteration of the loop. This function should be written
as follows.
int loopdemo(int n)
{
for(int i = 0; i < n; i++)
{
doSomething(i);
}
finish(n);
}
|
Do not change the value of a for-loop control variable in the loop body [6 points each, 3% max]
A for-loop
control variable (any variable that is modified in the third
part of a for-loop heading) should only be modified in the for-loop heading,
not in the body of the loop. For example, do not write
for(i = 1; i < n; i++)
{
...
i = n;
...
}
If you want to break out of a loop, use break or return.
|
Do not change a for-loop end value in the loop without justification [6 points each, 3% max]
Do not change the end-value of a for-loop just as a way to get
out of the loop. For example,
for(i = 1; i < n; i++)
{
...
if(condition)
{
n = 0;
}
...
}
is not a good way to cause the loop to end. If you want to
exit a for-loop, use break or return.
|
Initialize for a for-loop in the heading where sensible [4 points each, 1% max]
The first component of a for-loop heading is for initializing the
control variable. Use it unless you have a good reason for
not using it. For example, do not write
int i = 1;
for(; i < n; i++)
{
...
|
Update the variable controlled by a for-loop heading in the for-loop heading where sensible [4 points each, 1% max]
The third component of a for-loop heading is for updating the
control variable. Use it unless you have a good reason for
not using it. For example, do not write
for(int i = 1; i < n;)
{
...
i++;
}
|
Where sensible, a for-loop heading should control one variable [5 points each, 2% max]
Loop
for(int k = 2; k <= n; p = p * x)
{
k++;
}
does some of the control of k in the loop heading and some
in the body. Instead, put all of the control of k in the
loop heading.
for(int k = 2; k <= n; k++)
{
p = p * x;
}
|