C++ if, if…else and Nested if…else

C++ if, if…else and Nested if…else: In this article, you will learn to make a decision-making statement in a C++ program using various types of if..else statements.

In computer programming, we use the if statement to run a square code just when a specific condition is met.

For instance, assigning grades (A, B, C) in view of imprints acquired by a student.

if the percentage is above 90, assign grade A
if the percentage is above 75, assign grade B
if the percentage is above 65, assign grade C

There are three forms of if…else statements in C++.

1. if statement
2. if…else statement
3. if…else if…else statement

C++ if Statement

The syntax of the if statement is:

``````if (condition) {
// body of if statement
}``````

The if statement evaluates the condition inside the parentheses ( ).

If the condition evaluates to true, the code inside the body of if is executed.
If the condition evaluates to false, the code inside the body of if is skipped.
Note: The code inside { } is the body of the if statement.

Example 1: C++ if Statement

``````// Program to print positive number entered by the user
// If the user enters a negative number, it is skipped

#include <iostream>
using namespace std;

int main() {
int number;

cout << "Enter an integer: ";
cin >> number;

// checks if the number is positive
if (number > 0) {
cout << "You entered a positive integer: " << number << endl;
}
cout << "This statement is always executed.";
return 0;
}
``````

Output 1

``````Enter an integer: 5
You entered a positive number: 5
This statement is always executed.``````

At the point when the user enters 5, the condition number > 0 is assessed to valid and the announcement inside the assortment of if is executed.

Output 2

``````Enter a number: -5
This statement is always executed.``````

At the point when the user enters – 5, the condition number > 0 is assessed to bogus and the announcement inside the collection of if isn’t executed.

C++ if…else

The if statement can have an optional else clause. Its syntax is:

``````if (condition) {
// block of code if condition is true
}
else {
// block of code if condition is false
}``````

The if..else statement evaluates the condition inside the parenthesis.

If the condition evaluates true,

the code inside the body of if is executed
the code inside the body of else is skipped from execution
If the condition evaluates false,

the code inside the body of else is executed
the code inside the body of if is skipped from execution

Example 2: C++ if…else Statement

``````// Program to check whether an integer is positive or negative
// This program considers 0 as a positive number

#include <iostream>
using namespace std;

int main() {
int number;

cout << "Enter an integer: ";
cin >> number;
if (number >= 0) {
cout << "You entered a positive integer: " << number << endl;
}
else {
cout << "You entered a negative integer: " << number << endl;
}
cout << "This line is always printed.";
return 0;
}``````

Output

``````Enter an integer: 4
You entered a positive integer: 4.
This line is always printed.``````

In the above program, we have the condition number >= 0. On the off chance that we enter the number more prominent or equivalent to 0, at that point the condition assesses valid.

Here, we enter 4. so, the condition is valid. Thus, the announcement inside the assemblage of if is executed.

Output 2

``````Enter an integer: -4
You entered a negative integer: -4.
This line is always printed.``````

Here, we enter -4. So, the condition is false. Hence, the statement inside the body of else is executed.

C++ if…else…else if statement

The if…else statement is used to execute a square of code among two other options. In any case, if we have to settle on a decision between multiple other options, we use the if…else statement.

The syntax of the if…else statement is:

``````if (condition1) {
// code block 1
} else if (condition2){
// code block 2
} else {
// code block 3
}``````

Here,

If condition1 evaluates to true, the code block 1 is executed.
If condition1 evaluates to false, then condition2 is evaluated.
If condition2 is true, the code block 2 is executed.
If condition2 is false, the code block 3 is executed.

Note: There can be more than one else if statement yet just one if and else statements.

Example 3: C++ if…else…else if

``````// Program to check whether an integer is positive, negative or zero

#include <iostream>
using namespace std;

int main() {
int number;

cout << "Enter an integer: ";
cin >> number;
if (number > 0) {
cout << "You entered a positive integer: " << number << endl;
}
else if (number < 0) {
cout << "You entered a negative integer: " << number << endl;
}
else {
cout << "You entered 0." << endl;
}
cout << "This line is always printed.";
return 0;
}``````

Output 1

``````Enter an integer: 1
You entered a positive integer: 1.
This line is always printed.``````

Output 2

``````Enter an integer: -2
You entered a negative integer: -2.
This line is always printed.``````

Output 3

``````Enter an integer: 0
You entered 0.
This line is always printed.``````

In this program, we take a number from the user. We at that point use the if…else stepping stool to check whether the number is sure, negative, or zero.

In the event that the number is more noteworthy than 0, the code inside the if square is executed. In the event that the number is under 0, the code inside the else if square is executed. Something else, the code inside the else square is executed.

C++ Nested if…else

Once in a while, we have to use an if statement inside another if statement. This is known as settled if statement.

Consider its various layers of if statement. There is a first, external if explanation, and inside it is another, internal if statement. Its syntax is:

``````// outer if statement
if (condition1) {
// statements

// inner if statement
if (condition2) {
// statements
}
}``````

Notes:

We can add else and else if statements to the inner if statement as required.
The inner if statement can also be inserted inside the outer else or else if statements (if they exist).
We can nest multiple layers of if statements.

Example 4: C++ Nested if

``````// C++ program to find if an integer is even or odd or neither (0)
// using nested if statements

#include <iostream>
using namespace std;

int main() {
int num;

cout << "Enter an integer: ";
cin >> num;

// outer if condition
if (num != 0) {

// inner if condition
if ((num % 2) == 0) {
cout << "The number is even." << endl;
}
// inner else condition
else {
cout << "The number is odd." << endl;
}
}
// outer else condition
else {
cout << "The number is 0 and it is neither even nor odd." << endl;
}
cout << "This line is always printed." << endl;
}``````

Output 1

``````Enter an integer: 34
The number is even.
This line is always printed.``````

Output 2

``````Enter an integer: 35
The number is odd.
This line is always printed.``````

Output 3

``````Enter an integer: 0
The number is 0 and it is neither even nor odd.
This line is always printed.``````

In the above example,

We take an integer as an input from the user and store it in the variable num.
We then use an if…else statement to check whether num is not equal to 0.
If true, then the inner if…else statement is executed.
If false, the code inside the outer else condition is executed, which prints “The number is 0 and neither even nor odd.”
The inner if…else statement checks whether the input number is divisible by 2.
If true, then we print a statement saying that the number is even.
If false, we print that the number is odd.

Notice that 0 is additionally divisible by 2, however, it is really not a much number. This is the reason we first ensure that the information number isn’t 0 in the outer if condition.

Note: As you can see, settled if…else makes your rationale confused. On the off chance that conceivable, you should always try to avoid nested if…else.

Body of if…else With Only One Statement

If the body of if…else has only one statement, you can omit { } in the program. For example, you can replace

``````int number = 5;

if (number > 0) {
cout << "The number is positive." << endl;
}
else {
cout << "The number is negative." << endl;
}``````

With

``````int number = 5;

if (number > 0)
cout << "The number is positive." << endl;
else
cout << "The number is negative." << endl;``````

The output of the two programs will be the equivalent.

Note: Although it’s not important to use { } if the assemblage of if…else has just a single statement, using { } makes your code more clear.

Please feel free to give your comment if you face any difficulty here.