if else_if else - learn Dart

In dart, we found two type of decision controlling instructions – if-else statements and switch statements. Here we will discuss about if-else part of dart. We put conditions into if/else-if statements. Condition gets Boolean expression which returns either true or false.

if statement

In dart, for decisions control we can use if statements.

Syntax –

if (condition){
statements;
statements;
}

Let’s see some coding examples…

Write a code, which will check integer variable ‘a’ value is 10 or not.

Code 1:

void main(){
int a=10;
// simple if
if (a==10) {
print(‘a is 10’);
}
}

output

Write a code, which will check String variable ‘name’ value “microcodes” or not.

Code 2:

void main(){
String name;
name=”microcodes”;
// check both string equal or not.
if (name==”microcodes”) {
print(‘string matched!’);
}
}

output

Nested if

It’s simply means if statement inside another If statement. When we have multiple conditions then sometime we can use nested if block. Let’s understand through an example…

Syntax –

If(condition1){
If(condition2){
Statements;
} }

Make a code using nested-if statements, which will response on those persons which age between 18-30.

Code 3:

void main(){
int age=22;

if (age>=18) {
    // nested if
    if (age<=30) {
      print(‘age between 18-30’);
      print(‘age is’);
      print(‘$age’);
    }
}
}

output

Else statement

When if block’s condition not satisfies then else block get executed.

Syntax –

if (condition){
statements;
}
else{
statements;
}

Let’s understand through a coding example…

Code 4:

void main(){
int a=23;
if (a==90) {
    print(‘a is 90’);
}
else {
    // else block
    print(‘a is 23’);
}
}

output

Write a code, which checks if name will ‘bill’ then print message ‘bill invented windows’; else name will ‘linus’ then print message ‘linus invented linux kernel’.

Code 5:

import ‘dart:io’;

void main(){
String? name;

print(‘Enter Name: ‘);
name=stdin.readLineSync();

if (name==”bill”) {
print(‘bill invented windows’);
}
else{
print(‘linus invented linux kernel’);
}
}

output

Write a code, which checks a double variable ‘per’, value is 80.5 or not.

Code 6:

import ‘dart:io’;

void main(){
String? str;
late double per;

// getting string input
print(‘Enter value: ‘);
str=stdin.readLineSync();
if (str!=null) {
    // converts string->double
    per=double.parse(str);
}

// condition checks
if (per==80.4) {
    print(‘percentage is 80.4’);

} else {
    print(‘percentage is 80.5’);

}
}

output

Else if statement

When we want to handle multiple conditions, then we can use else-if statements. Let’s understand use case of else-if statements.

Syntax –

if (condition){
statements;
}
else if (condition){
statements;
}

Make a code, where it takes user’s phone number country code. There have three countries – India (91), Pakistan (92), and Bangladesh (93). According to user’s input it will print user’s country.

Code 7:

import ‘dart:io’;

void main(){
String? str;
late int a;

// taking input
print(‘Enter Country code: ‘);
str=stdin.readLineSync();
// converts String->int
if (str!=null) {
    a=int.parse(str);
}

// country code condition checks
   if (a==91) {
     print(‘india’);
   }
   else if(a==92){
    print(‘Pakistan’);
   }
     else if(a==93){
    print(‘bangladesh’);
   }}

output

Nested if-else statement

When we want to handle multiple conditions then we can use nested if-else statements.

Let’s understand through below code example…

Code 8:

import ‘dart:io’;
// A code, which return message ‘got it!’, if value between -5 to +5
void main(){
String? str;
late int a;

print(‘Enter value: ‘);
str=stdin.readLineSync();
if (str!=null) {
    a=int.parse(str);
}

if (a>=-5) {
    // nested if-else block
    if (a<=5) {
      print(‘got it!’);
    }
    else{
      print(‘2nd condition not match!’);
    }
}
else{
    print(‘enter valid number!’);
}
}

output

Work with Logical Operators

Till now, we have seen if, else if, else statements using relational operators like > (greater than) <(less than) >=(greater than equal) !=(not equal) etc.

Now we will perform logical operations over if-else statements.

Logical AND [ && ] – if both inputs same then output same.

Code 9:

import ‘dart:io’;

void main(){
String? str;
late int a;

print(‘Enter value: ‘);
str=stdin.readLineSync();
if (str!=null) {
    a=int.parse(str);
}

// checks integer(a) between 20 – 30
if (a>=20 && a<=30) {
    print(‘a between 20 and 30’);
}
else{
    print(‘condition not match!’);
}
}

output

Write a code, which will check a string name start with ‘linus’ and end with ‘torvalds’.

Code 10:

import ‘dart:io’;

void main(){
String? fname,lname;

print(‘Enter first name: ‘);
fname=stdin.readLineSync();
print(‘Enter last name: ‘);
lname=stdin.readLineSync();

if (fname==”linus” && lname==”torvalds”) {
    print(‘name is’);
    print(‘$fname $lname’);
    print(‘invented linux’);
}
else{
    print(‘oops!’);
}
}

output

Logical OR – if at-least one input gets true then output same. This can be represented as ||

Let’s see logical OR operation, with integers of it…

Code 11:

import ‘dart:io’;

void main(){
String? str;
int a=10;

print(‘Enter value: ‘);
str=stdin.readLineSync();
if (str!=null) {
    a=int.parse(str);
}

// first condition a==20(false) but a==10(true)
if (a==20 || a==10) {
    print(‘a either 20 or 10’);
}
else{
    print(‘condition not match!’);
}
}

output

Let’s see logical OR operation on String

Code 12:

import ‘dart:io’;

void main(){
String? str; var name;

print(‘Enter String: ‘);
str=stdin.readLineSync();
name=str;
// first condition name==’java'(false) but name==’false'(true)
if (name==”java” || name==”dart”) {
print(‘name either java or dart lang.’);
}
else{
print(‘condition not match!’);
}
}

output

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