3.2. While Loops¶
As we noted earlier, algorithms require two important control structures: iteration and selection. Both of these are supported by Python in various forms. The programmer can choose the statement that is most useful for the given circumstance.
For repeating a block of code, C++ provides a standard while and for constructs.
The while construct repeats a body of code as long as a condition is true. For example,
int counter = 1;
while (counter <= 5) { /*Use of an interactive method until the
the loop ends */
cout << "Hello, world" << endl;
counter = counter + 1;
}
Console output:
Hello, world
Hello, world
Hello, world
Hello, world
Hello, world
prints out the phrase “Hello, world” five times. The condition on the
while statement is evaluated at the start of each repetition. If the
condition is true, the body of the statement will execute.
The while statement is a very general purpose iterative structure
that we will use in a number of different algorithms. In many cases, a
compound condition will control the iteration. A fragment such as
while ((counter <= 10) && (!done)) {
...
would cause the body of the statement to be executed only in the case
where both parts of the condition are satisfied due to the and operator (&&). The value of the
variable counter would need to be less than or equal to 10 and the
value of the variable done would need to be false (not false
is true) so that true and true results in true.
Here are some of the logical operators that are useful for true-false boolean statements in C++.
and - &&
or - ||
not equal to - !=
not - !
greater than - >
less than - <
greater than
or equal to - >=
less than
or equal to - <=
These are the same as we saw in earlier chapters.
#include <iostream>
using namespace std;
int main(){
int counter = 0;
while (counter <= 1) {
cout << "Hello, world!" << endl;
}
};
- "0" is written 1 time.
- Take a look at the cout line.
- "Hello world!" is written 1 time.
- Take a closer look at the while loop
- "Hello world!" is written infinitely many times.
- Right! because counter is never greater than one, thus making the while loop infinite.
- None of the above.
- Not quite, take another look.
Q-1: Using the code above please select the answer that should appear.