- What the if-else statement is and why it matters in C
- How to write if-else syntax correctly
- How to check even/odd numbers using if-else
- How to use flowcharts to understand program flow
Understanding the C if-else Statement
In C programming, the if-else statement is a decision-making statement. This statement decides whether the statements or block of code should be executed or not based on conditions. It is one of the simplest and most important conditional statements in C language.
Using the if-else statement, the flow of execution of a program can be changed or modified. Basically, the if-else statement controls the flow of a program and is also termed a control flow statement. It decides whether a certain statement or block of statements will be executed or not based on a given condition.
For example, if a given condition is true, then the statements or block of statements inside the if body are executed; otherwise, the code in the else block will be executed. if-else allows code to be executed conditionally based on a boolean condition. if-else statements make the block of code more readable.
How the if-else Statement Works
If the "condition" is true:
• The statements inside the body of the if control statement are executed.
• Statements inside the body of the else statement are ignored.
If the "condition" is false:
• The statements inside the body of the if are ignored.
• Statements inside the else part are executed.
Syntax: if-else Statement
if (condition)
{
// if body
// Statements to execute if condition is true
}
else
{
// Statements to execute if condition is false
}
Step-by-step execution:
1. The program control first reaches the if statement and tests the condition.
2. If the test condition is true: The if block is executed.
3. If the test condition evaluates to false: The else block is executed.
4. Afterward, the program control continues to the remaining statements below inside the program.
5. The condition in the syntax evaluates to true (i.e., 1) or false (i.e., 0).
The C language instructions or statements can be a single line or multiple lines of code enclosed within curly braces { }.
Flowchart: if-else Statement
The diagram illustrates the syntax and flowchart of the if-else statement.
How it works:
1. If the tested condition is true, then the statements inside the if block are executed.
2. If the tested condition is false, then the code or statements inside the else block are executed.
Note that "statements outside if" always execute regardless of whether the condition is true or false.
Example 1: C Program to Check Even or Odd
/* C program to check if a given number is even or odd using if-else statement */
#include <stdio.h>
int main()
{
int x;
printf("\n Enter any number: ");
scanf("%d", &x);
if(x % 2 == 0) /* test-condition */
{
printf("\n %d is an even number", x);
}
else /* else executes when condition is false */
{
printf("\n %d is an odd number", x);
}
return 0;
}
/* Output:
Enter any number: 7
7 is an odd number */Program Explanation
The above program demonstrates the use of an if-else statement to determine whether a given number is even or odd.
1. First, we declare an integer variable int x; to store the number entered by the user.
2. Next, we use printf("\n Enter any number"); to display a prompt on the screen, and scanf("%d", &x); to read the user's input. In this example, the user enters 7, which is stored in the variable x.
3. The program then evaluates the if condition x % 2 == 0 to check whether the number is even or odd. Since 7 % 2 gives a remainder of 1, the condition x % 2 == 0 evaluates to false.
4. Because the condition is false, the else block is executed. The statement printf("\n %d is an odd number", x); runs, and the output displayed is: "7 is an odd number".
Note: The %d is a format specifier that acts as a placeholder for the integer value of x. It is replaced with the actual value 7 when the output is displayed, resulting in the message: "7 is an odd number".
💻 Practice Exercise
Challenge: Write a program that checks if a number is positive, negative, or zero using if-else statement.
🔍 Click to Show Solution
#include <stdio.h>
int main() {
int num;
printf("Enter a number: ");
scanf("%d", &num);
if(num > 0) {
printf("%d is a positive number\n", num);
}
else if(num < 0) {
printf("%d is a negative number\n", num);
}
else {
printf("The number is zero\n");
}
return 0;
}
Expected Output:
Enter a number: -5
-5 is a negative number
Frequently Asked Questions About if-else in C
1. What is the difference between if and if-else in C?
The if statement executes code only when the condition is true. The if-else statement executes one block when the condition is true and another when it is false.
2. Can I use multiple conditions in if-else?
Yes, you can combine multiple conditions using logical operators like && (AND) and || (OR). You can also use nested if-else or if-else ladder for multiple conditions.
3. Is else mandatory with if in C?
No, the else block is optional. You can use if alone when you only need to execute code when a condition is true.