The while loop

There are times when we  need to execute a code segment repeatedly based on a condition. Solidity provides while loops precisely for this purpose. The general form of the while loop is as follows:

Declare and initialize a counter
while (check the value of counter using an expression or condition) {
    Execute the instructions here
    Increment the value of counter
}

while is a keyword in Solidity and it informs the compiler that it contains a decision control instruction. If this expression evaluates to true then the code instructions that follow in the pair of double-brackets { and } should be executed. The while loop keeps executing until the condition turns false. 

In the following example, mapping is declared along with counter. counter helps loop the mapping since there is no out-of-the-box support in Solidity to loop mapping...