C++ for Scientists - Technische Universität Dresden

36 CHAPTER 2. C++ BASICS
eps/= 2.0;
} while (eps > 0.0001);
The loop is performed at least one time — even with an extremely small value for eps in our
example. The difference between a while-loop and a do-while-loop is irrelevant to most scientific
software. Only loops with very few iterations and with extremely strong impact on the overall
performance might matter because a do-while-loop performs one comparison and one jump less.
2.5.4 For Loop
The most common loop in C ++ is the for-loop. As simple example we like to add two vectors 15
and print the result afterward:
double v[3], w[]= {2., 4., 6.}, x[]= {6., 5., 4};
for (int i= 0; i < 3; i++)
v[i] = w[i] + x[i];
for (int i= 0; i < 3; i++)
cout ≪ ”v[” ≪ i ≪ ”] = ” ≪ v[i] ≪ ’\n’;
The loop head consists of three components:
• The initialization;
• A Continuation criterion; and
• A step operation.
The example above is typical for a for-loop. In the initialization, one typically declares a new
variable and initializes it to 0 because this is the start index of most indexed data structures.
The condition usually tests if the loop index is smaller than a certain size and the last operation
typically increments the loop index.
It is a very popular beginners’ mistake to write conditions like “i