In this chapter, we will discuss in detail definite and indefinite loops in TypeScript .
Sometimes you face situations when you want a block of code to run several times in your program. In general, statements run consecutively. The first statement in a function runs first, follows by the second, and so on.
Programming languages give many control systems that allow for more complex execution paths.
A loop statement lets us run a statement or group of statements multiple times. You can see the general form of a loop statement given below in most of the programming languages.
TypeScript gives different kinds of loops to control looping requirements. The following figure shows the classification of loops.
Definite Loop
A loop whose number of repetitions is fixed is known as a definite loop . The for loop is an application of a definite loop.
S.No. Loop Name Loops & Description 1. for The for loop is an implementation of a definite loop.
Indefinite Loop
An indefinite loop is used when the number of repetitions in a loop is unknown.
Indefinite loops can be implemented using.
S.No Loop Name Loops & Description 1. while The while loop executes the instructions each time the condition specified evaluates to true. 2. do…while The do…while loop is similar to the while loop except that the do…while loop doesn’t evaluate the condition for the first time the loop executes.
Example: while versus do..while
var n:number = 5
while(n > 5) {
console.log("Entered while")
}
do {
console.log("Entered do…while")
}
while(n>5)
The example at first declares a while loop. The loop enters only if the expression passes to while seems to be true. In this example, the value of n is not greater than zero. Therefore, the expression returns false and the loop will not run.
On the other hand, the do…while loop runs the statement once because the initial repetition does not consider the Boolean expression. However, the while loops check the condition and take the control out of the loop for the consecutive repetition.
It will run following JavaScript code on composing.
//Generated by typescript 1.8.10
var n = 5;
while (n > 5) {
console.log("Entered while");
}
do {
console.log("Entered do…while");
} while (n > 5);
The above code will produce the following output.
The break Statement
The break statement allows us to take control out of a setup. If we use a break in a loop, it will cause the program to exit the loop. Its syntax is as follows.
Syntax
Flow diagram
Example
Now, take a look at the following example code.
var i:number = 1
while(i<=10) {
if (i % 5 == 0) {
console.log ("The first multiple of 5 between 1 and 10 is : "+i)
break //exit the loop if the first multiple is found
}
i++
} //outputs 5 and exits the loop
On compiling, it will generate the following JavaScript code.
//Generated by typescript 1.8.10
var i = 1;
while (i <= 10) {
if (i % 5 == 0) {
console.log("The first multiple of 5 between 1 and 10 is : " + i);
break; //exit the loop if the first multiple is found
}
i++;
} //outputs 5 and exits the loop
It shows the following output.
The first multiple of 5 between 1 and 10 is : 5
The continue Statement
The continue statement jumps the subsequent statements in the current repetition and takes the control back to the beginning of the loop. It does not exit the loop, unlike the break statement. . It ends the current repetition and starts the following repetition.
Syntax
Flowchart
Example
An example of the continue statement is given below.
var num:number = 0
var count:number = 0;
for(num=0;num<=20;num++) {
if (num % 2==0) {
continue
}
count++
}
console.log (" The count of odd values between 0 and 20 is: "+count) //outputs 10
The above example shows the number of odd values between 0 and 20. The loop exits the current repetition if the number is even. The continue statement helps us to get this.
It runs following JavaScript code on compiling.
//Generated by typescript 1.8.10
var num = 0;
var count = 0;
for (num = 0; num <= 20; num++) {
if (num % 2 == 0) {
continue;
}
count++;
}
console.log(" The count of odd values between 0 and 20 is: " + count); //outputs 10
Output
The count of odd values between 0 and 20 is: 10
The Infinite Loop
An infinite loop is a loop that runs infinitely. The for loop and the while loop are used to make an endless loop.
Example: Infinite loop using for loop
for(;;) {
console.log(“This is an endless loop”)
}
Syntax: Infinite loop using while loop
while(true) {
//statements
}
Example: Infinite loop using while loop
while(true) {
console.log(“This is an endless loop”)
}
