If-Else Statement in C++

In this tutorial, we will learn about if-else statements in C++. We will cover the basics of conditional execution using if-else statements.

What is an If-Else statement

An if-else statement is a conditional statement that executes one block of code if a specified condition is true, and another block of code if the condition is false.

Syntax

The syntax for the if-else statement in C++ is:

if (condition) {
    // Code block to execute if condition is true
} else {
    // Code block to execute if condition is false
}

The if-else statement evaluates the specified condition. If the condition is true, the code block inside the if statement is executed; otherwise, the code block inside the else statement is executed.

The following is the flowchart of how execution flows from start to the end of an if-else statement.

Flowchart of If Else Statement

Example 1: Checking if a Number is Even or Odd

  1. Declare an integer variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is even or odd.
  4. Print a message indicating whether num is even or odd.

C++ Program

#include <iostream>
using namespace std;
int main() {
    int num = 10;
    if (num % 2 == 0) {
        cout << num << " is even.";
    } else {
        cout << num << " is odd.";
    }
    return 0;
}

Output

10 is even.

Example 2: Checking if a String Starts with a Specific Value

  1. Declare a string variable str.
  2. Assign a value to str.
  3. Use an if-else statement to check if str starts with a specific value.
  4. Print a message indicating the result of the check.

C++ Program

#include <iostream>
#include <string>
using namespace std;
int main() {
    string str = "Hello, world!";
    if (str.substr(0, 5) == "Hello") {
        cout << "String starts with 'Hello'.";
    } else {
        cout << "String does not start with 'Hello'.";
    }
    return 0;
}

Output

String starts with 'Hello'.

Example 3: Checking if a Number is Positive or Negative

  1. Declare an integer variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is positive or negative.
  4. Print a message indicating whether num is positive or negative.

C++ Program

#include <iostream>
using namespace std;
int main() {
    int num = -5;
    if (num > 0) {
        cout << num << " is positive.";
    } else {
        cout << num << " is negative or zero.";
    }
    return 0;
}

Output

-5 is negative or zero.