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Do while loop
Here, in this section, we will discuss the do-while loop in C++. Do while is a looping structure in C++, these types of loops are called Exit control or Post-test loops.


Looping in C++
We have the following loops in C++ :
- While loop
- For loop
- Do while
- Nested loops
We will discuss do-while loop in this post –
Do while
Very similar to the while loop. To do repetitive work control structure has been created.
In do while we execute some statements first and then check a condition. If the condition is met we execute it again. We keep doing this until the condition keeps meeting.
Syntax
do{ // execute statement(s) }while(condition(s))
Along with increment and initialization logic it may look like 0
initialization; do{ // execute statement(s) incrementation; }while(condition(s))


Let us learn do-while looping with a few examples –
Example 1
#include<iostream> using namespace std; int main() { int i = 1; // initialization do{ cout << i << ". Hello World\n"; i++; // incrementation }while(i <= 5); // condition(s) checking return 0; }
Output
1. Hello World 2. Hello World 3. Hello World 4. Hello World 5. Hello World
The reason to this is that we first do i.e. execute statements and then after it we do condition checking to check if we need to implement the statements again or not.
The following examples show how it will be implemented at least once –
Example 1.1
#include<iostream> using namespace std; int main() { int i = 1000; // i is set as 1000 which is definitely greater than 5 // the condition set below is (i <= 5) which will surely be never met // as the loop is incrementing (i++) // but still the loop is executed once anyways do{ cout << i << ". Hello World\n"; i++; }while(i <= 5); return 0; }
Output
1000. Hello World
Example 2
Program to print first n numbers.
#include<iostream> using namespace std; int main() { int n = 25; int i = 1; do{ cout << i << " "; i++; }while(i <= n); return 0; }
Output
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Example 3
Program to print numbers divisible by 7 up to 100.
#include<iostream> using namespace std; int main() { int n = 100; int i = 1; do{ // if divisible by 7 must leave 0 remainder // on applying modulo operator if(i % 7 == 0){ cout << i << " "; } i++; }while(i <= n); return 0; }
Output
7 14 21 28 35 42 49 56 63 70 77 84 91 98
Example 4
Program to print items in a character array
#include<iostream> using namespace std; int main() { char a[] = {'P', 'o', 'k', 'e', 'm', 'o', 'n'}; int i = 0; // array index starts from 0 do{ cout << a[i] << " "; i++; }while(i < 7); return 0; }
Output
P o k e m o n
Example 5
Program to print Ascii Values
#include using namespace std; int main() { char i='A';//inialisation do { cout << i << " : " << (int) i << " "; i++; // ascii codes are incremented } while(i<='Z'); // internally ascicodes are compared }
Output
A : 65 B : 66 C : 67 D : 68 E : 69 F : 70 G : 71 H : 72 I : 73 J : 74 K : 75 L : 76 M : 77 N : 78 O : 79 P : 80 Q : 81 R : 82 S : 83 T : 84 U : 85 V : 86 W : 87 X : 88 Y : 89 Z : 90
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