Mastering the C If Statement: Essential for Conditional Execution

Explore the importance of the if statement in C programming for conditional execution. Understand how to use the optional else keyword to define actions based on whether conditions are true or false, enhancing your program's decision-making capabilities.

C - The If Statement

Conditional execution of instructions is fundamental in programming. The if statement in C is used for decision-making based on conditions. An optional else keyword can be used to specify actions if the condition is false.

Syntax of if Statement

The syntax for the if statement is as follows:

Syntax


if(boolean_expression) {
 /* statement(s) will execute if the boolean expression is true */
}

How if Statement Works

The if statement uses curly brackets to form a code block. If the boolean expression evaluates to true, the code block inside the if statement executes. If false, the code following the block executes.

In C, any non-zero and non-null values are considered true, while zero or null values are false.

Flowchart of if Statement

The flowchart for the if statement is as follows:

Example of if Statement in C

This example shows a basic use of the if statement, which checks if a variable is less than 20.

Code


#include 

int main() {
  int a;
  a = 12; // Change to 40 and run again
  printf("Value of a is : %d\n", a);
  if(a < 20) {
      printf("a is less than 20\n");
  }
  return 0;
}

Output


Value of a is : 12
a is less than 20

if Statement with Logical Operations

You can use logical operators && (AND) or || (OR) in the if statement.

Code


#include 

int main() {
  int a, b, c;
  a = 10; b = 5; c = 7; // Change to 10, 20, 15 and run again
  if (a >= b && a >= c) {
      printf("a is greater than b and c\n");
  }
  printf("a: %d b: %d c: %d\n", a, b, c);
  return 0;
}

Output


// When values for a, b, and c are 10, 5, 7
a is greater than b and c
a: 10 b: 5 c: 7

// When values for a, b, and c are 10, 20, 15
a: 10 b: 20 c: 15

Multiple if Statements

You can use multiple if statements to check different conditions. For example, calculating discounts based on the bill amount.

Code


#include 

int main() {
  int amount;
  float discount, net;
  amount = 500; // Change to 2250 and 5200 and run again
  if (amount < 1000) {
      discount = 0;
  }
  if (amount >= 1000 && amount < 5000) {
      discount = 5;
  }
  if (amount >= 5000) {
      discount = 10;
  }
  net = amount - amount * discount / 100;
  printf("Amount: %d Discount: %f Net payable: %f\n", amount, discount, net);
  return 0;
}

Output


// When the bill amount is 500
Amount: 500 Discount: 0.000000 Net payable: 500.000000

// When the bill amount is 2250
Amount: 2250 Discount: 5.000000 Net payable: 2137.500000

// When the bill amount is 5200
Amount: 5200 Discount: 10.000000 Net payable: 4680.000000

Checking Multiple Conditions with if Statement

Multiple conditions can be checked using logical operators. For example, determining if a student passes based on average marks and individual subject marks.

Code


#include 

int main() {
  int phy, maths;
  float avg;
  phy = 50; maths = 50; // Change to 40, 40 and 80, 40
  avg = (float)(phy + maths) / 2;
  printf("Phy: %d Maths: %d Avg: %f\n", phy, maths, avg);
  if (avg >= 50 && (maths >= 35 && phy >= 35)) {
      printf("Result: Pass\n");
  }
  if (avg < 50) {
      printf("Result: Fail\n");
  }
  return 0;
}

Output


// When marks in Phy and Maths are 50 and 50
Phy: 50 Maths: 50 Avg: 50.000000
Result: Pass

// When marks in Phy and Maths are 40 and 40
Phy: 40 Maths: 40 Avg: 40.000000
Result: Fail

// When marks in Phy and Maths are 80 and 40
Phy: 80 Maths: 40 Avg: 60.000000
Result: Pass