Loop Exit Conditions

Loop exit conditions determine the number of iterations that a loop executes. For example, fixed indexes for loops determine the iterations. The loop iterations must be countable; that is, the number of iterations must be expressed as one of the following:

a constant
a loop invariant term
a linear function of outermost loop indices

Loops whose exit depends on computation are not countable. Examples below show countable and non-countable loop constructs.

Correct Usage for Countable Loop

// Exit condition specified by "N-1b+1"

count=N;

...

while(count!=1b)

{

// 1b is not affected within loop

a[i]=b[i]*x;

b[i]=[i]+sqrt(d[i]);

--count;

}

Correct Usage for Countable Loop

// Exit condition is "(n-m+2)/2"

i=0;

for(l=m; l<n; l+=2)

{

a[i]=b[i]*x;

b[i]=c[i]+sqrt(d[i]);

++i;

}

Incorrect Usage for Non-Countable Loop

i=0;

// Iterations dependent on a[i]

while(a[i]>0.0)

{

a[i]=b[i]*c[i];

++i;

}