If Statement in C

An if statement in C is one of the most important control structures that is used to make decisions based on the given conditions. It helps developers to control the flow of a program by executing a particular block of code only when the condition is true. So, whether you are creating login systems, game logic, or real-time decision-making programs, using the if statement is important and helpful. In this article, we will discuss what an if statement in C is, its syntax, working, flow diagram, examples, benefits, drawbacks, common mistakes, and real-life applications.

Table of Contents:

• What is an if Statement in C?
• Syntax of an if Statement in C
• How does an if Statement Work in C?
• Flow Diagram of C if Statement
• Examples of if Statements in C
• Benefits of the C if statement
• Drawbacks of the C if Statement
• Nested if Statement in C
• Common Mistakes When Using If Statements in C
• Real-Life Applications of the if Statement
• Conclusion

What is an if Statement in C?

An if statement in C is a conditional control statement that is used to execute a block of code only if a specified condition is true. If the condition is true, the code inside the if block runs; otherwise, it is skipped. This helps to control the flow of the program, which is based on different situations. It is one of the basic structures that is used for decision-making in C programming. 

Syntax of an if Statement in C

The syntax of an if statement in C programming is as follows:

if (condition) {
    // Code to execute if the condition is true
}

Here,

• The condition inside the parentheses is evaluated as either true or false.
• If the condition is true, the block of code inside the { } runs.
• If the condition is false, the code block is skipped.

Example:

Output:

The code shows that the program checks if the variable number is greater than 5, and if it is true, then it prints a message to the console.

How does an if Statement Work in C?

Here is a step-by-step description of how the if statement in C:

Step 1: Condition Evaluation

• This is the first step, in which the expression inside the if statement is checked to see whether it is true or false.
• Example: if (number > 5) -> checks whether number is greater than 5.

Step 2: Decision

• If the condition is true, then the program will decide to execute the code block.
• If the condition is false, then the program will decide to skip the block.

Step 3: Execution Flow

• If the condition is true, then the control enters the {} block and runs the code.
• If the condition is false, then the control jumps past the if block and continues with the rest of the program.

Let’s understand the working of the if statement in C with the help of an example.

Output:

In this program, the output is evaluated and printed in such a way;

1. Condition Evaluation
temperature > 25 -> 30 > 25 -> true

2. Decision
Since the condition is true, the program executes the if block.

3. Execution Flow
Prints: It’s a hot day.
Then continues to print: Program ended.

Flow Diagram of C if Statement

Here is the flowchart of the C if statement that will help to understand its working flow.

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Examples of if Statements in C

Here are a few examples of if statements in C that will help you understand how they can be used in different cases:

Example 1: Check a Positive Number

Output:

The above program checks if the variable “number” is greater than 0, and if it is true, then it prints “The number is positive” to the console.

Example 2: Check Voting Eligibility

Output:

The above program checks whether the variable “age” is 18 or greater, and if it is true, then it prints “You are eligible to vote.” to the console.

Example 3: Number is Even

Output:

The above program checks if the variable “number” is divisible by 2 or not using the modulus operator. If the given number is divisible by 2, then the condition is true; therefore, “The number is even” is printed to the console.

Example 4: Check if a Year is a Leap Year

Output: 

The above program shows how the if statement is used to check whether the year 2024 is a leap year using if statements. It prints “2024 is a leap year” if the year is divisible by 400 or divisible by 4 but not by 100; otherwise, it will print “2024 is not a leap year” to the console.

Example 5: Check Whether a Character is a Vowel

Output:

The above program uses multiple if statements that test whether the character “ch” is assigned to a vowel (upper-case or lower-case). If it finds a match, then the program prints to the user that the character is a vowel.

Benefits of the C if statement

1. The if statement in C is very simple and easy to understand because of its simple syntax.
2. It allows a program to make decisions and react differently due to different conditions at different points of execution.
3. The if statement helps control the flow of the program by executing the particular code when its condition is true.
4. It makes logic easier and more efficient by separating conditions.
5. It is possible to combine the if statement with other structures (else, else if, and iterators) to make logic more flexible and efficient.
6. The if statement will avoid executing unnecessary code, and thus it improves the program’s performance.
7. The if statement in C is also used to check for invalid or unexpected conditions or errors, to handle them safely.

Drawbacks of the C if Statement

• When using many if blocks, it may make your code more difficult to read and maintain.  
• It can be easy to confuse checks for conditions and make mistakes, especially with nested if statements.  
• For large sets of conditions or on large-scale applications, if statements are not scalable; switch or function pointers may be more efficient. 
• The code logic that is repeated within multiple if blocks will lead to redundant code that is difficult to maintain.  
• The repeated evaluations of conditions will slow the execution of the program in real-time high-performance programs.  

Nested if Statement in C

A nested if statement in C is a decision-making statement in which an if statement is placed inside another if statement. It allows checking one condition within the scope of another, which enables more specific decision-making. Also, the inner if statement runs only if the outer condition is true. A nested if statement is used for checking multiple dependent conditions.

Syntax: 

if (condition1) {
    if (condition2) {
        // Code runs if both condition1 and condition2 are true
    }
}

Example:

Output:

The above program shows how nested if statements are used to check if the given number is positive and even. If both conditions are true, then it prints “The number is positive and even”.

Common Mistakes When Using if Statements in C

1. Using = instead of == to check for equality.
2. Missing braces {} when writing multiple statements.
3. Writing confusing logical operators &&, ||, and !.
4. Not accounting for the cases with an else or else if.
5. Incorrect nesting, or inconsistent indentation.
6. Floating-point values should be compared using a tolerance ue to floating-point precision limitations.

Real-Life Applications of the if Statement

1. You can use an if statement in C programming to check if a username and password are valid in the login systems according to the initial usernames and passwords.
2. To know which light (red, yellow, or green) to turn on based on elapsed time or need for sensors in the traffic light control systems, an if statement is used.
3. You can use an if statement in the bank programs to confirm that a transaction is valid based on account balance or limits.
4. You can use an if statement in the e-commerce websites to provide discounts or a promotional offer based on user type or what was purchased.
5. To check a player’s health, score, or level in the game so that the events can be triggered on an action, you can use an if statement.
6. An if statement can also be used for sensor monitoring to trigger alarms or actions based on temperature, pressure, etc., if normal limits are exceeded. 

Conclusion

The if statement in C programming language is a basic control structure that helps programs in decision-making based on input and conditions. It is used to make the logic of programs better and easier for better efficiency, increase the readability of programs, and is also used in conditional logic or when execution is required. Whether if statements are used as login conditions or the use of nested if statements, they will help you write clear and efficient C programs.

If Statement in C – FAQs