While Loop:
· While loop executes a statement repeatedly unless and until the condition is fulfilled.· When the condition is found to be true, at that time the loop stop itself.
Format:
while (condition){
statement;
increment/decrement;
}
Example:
#include <iostream>
using namespace std;
int main(){
int a=1; //Here we initialize the variable ‘a’ from 1
while(a<6){ //Condition: That the loop runs upto 5 times.
cout<<"This is a while loop."<<endl; //This statement and the loop executes upto 5 iteration
a++; //And it will increment at the rate of 1. Equivalent to a=a+1
}
}
· After the loop completes 5 iteration, ‘a’ becomes 6, and the condition is evaluated to false and the loops stops running.
· We can use any increment value and we are also free to increment or decrement the variable used in looping.
For Loop:
· For loop is used when we exactly know the number of repetitions. It control the repetition structure and thus help us to write a loop that executes a specific number of times.Format:
for (variable initialization; condition; increment/decrement) {
statement;
}
Example:
#include <iostream>
using namespace std;
int main(){
int a; //Here we initialize the variable a from 1
for(a=1;a<=6;a++) { // we also directly specify the data type here: for(int a=1;a<=6;a++)
cout<<"Help"<<endl;
}
}
· At first the integer value initialize from 1.
· Then the condition specify that the loop run up to 5 iterations at the rate of 1 increment after each and every loop which is modifiable to a+=10, a-=3 or anything.
· After 5th iteration the condition is found to be false and thus the loop terminated.
Do While Loop:
· In do while loop the statement is defined at the top and the condition is defined at its bottom.· Thus unlike while loop, it executes at least one time due to predefined statement.
Format:
do {
statement;
}
while (condition);
Example:
#include <iostream>
using namespace std;
int main(){
int x=1; // integer variable initialized
do { // following statement executed first
cout<<"Check later"<<endl;
x+=5; // increment of 5 takes place
}
while (x<20); //condition:
}
· Loop runs 20 times according to the condition given i.e. it displays 4 iterations of "check later" statement.
· After the loop displays 4 iterations of that statement, then it found the condition to be false and hence it will terminate.
· And if the condition never evaluates to be false, then the statement runs forever.