Flow Diagram of while loop
Example 1: This program will try to print “Hello World” 5 times depending on a few conditions.
C++
// C++ program to illustrate while loop #include <iostream> using namespace std; int main() { // initialization expression int i = 1; // test expression while (i < 6) { cout << "Hello World\n" ; // update expression i++; } return 0; } |
Output:
Hello World Hello World Hello World Hello World Hello World
Dry-Run of Example 1:
1. Program starts. 2. i is initialized with value 1. 3. Condition is checked. 1 < 6 yields true. 3.a) "Hello World" gets printed 1st time. 3.b) Updation is done. Now i = 2. 4. Condition is checked. 2 < 6 yields true. 4.a) "Hello World" gets printed 2nd time. 4.b) Updation is done. Now i = 3. 5. Condition is checked. 3 < 6 yields true. 5.a) "Hello World" gets printed 3rd time 5.b) Updation is done. Now i = 4. 6. Condition is checked. 4 < 6 yields true. 6.a) "Hello World" gets printed 4th time 6.b) Updation is done. Now i = 5. 7. Condition is checked. 5 < 6 yields true. 7.a) "Hello World" gets printed 5th time 7.b) Updation is done. Now i = 6. 8. Condition is checked. 6 < 6 yields false. 9. Flow goes outside the loop to return 0.
Example 2:
C++
// C++ program to illustrate while loop #include <iostream> using namespace std; int main() { // initialization expression int i = 1; // test expression while (i > -5) { cout << i << "\n" ; // update expression i--; } return 0; } |
Output:
1 0 -1 -2 -3 -4
C++ While Loop
While Loop in C++ is used in situations where we do not know the exact number of iterations of the loop beforehand. The loop execution is terminated on the basis of the test condition. Loops in C++ come into use when we need to repeatedly execute a block of statements. During the study of the ‘for’ loop in C++, we have seen that the number of iterations is known beforehand, i.e. the number of times the loop body is needed to be executed is known to us.
Syntax:
while (test_expression) { // statements update_expression; }
The various parts of the While loop are:
- Test Expression: In this expression, we have to test the condition. If the condition evaluates to true then we will execute the body of the loop and go to update expression. Otherwise, we will exit from the while loop.
- Update Expression: After executing the loop body, this expression increments/decrements the loop variable by some value.
- Body: This is a group of statements that include variables, functions, and so on. With the while loop, code, and simple names can be printed, complex algorithms can be executed, or functional operations can be performed.
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