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Decision-Making Statements in C: From Basics to Advanced
Last Updated on: 24th Jul 2025 18:27:12 PM
Decision-making statements are the heart of any C program, allowing it to make choices based on conditions. Whether you're building a simple calculator or a complex game, these statements guide your code’s flow like a GPS for your program. In this tutorial, we’ll explore Simple if, if-else, Nested if-else, Ladder if (else-if ladder), and switch case, with examples ranging from beginner-friendly to advanced. Each example includes code, output, and a detailed explanation to make learning engaging and clear. Let’s get started!
1. Simple if Statement
The if statement evaluates a condition. If the condition is true, the code inside the if block executes. It’s like deciding to bring an umbrella if it’s raining.
Explanation: The condition temp >= 15 && temp <= 30 checks if the temperature is within a comfortable range. The && operator ensures both conditions are true. If false, the else block warns the user.
Syntax:
if (condition) {
// Code executes if condition is true
}
Basic Example: Check Voting Eligibility
#include <stdio.h>
int main() {
int age = 19;
if (age >= 18) {
printf("You are eligible to vote!\n");
}
return 0;
}
Output:
You are eligible to vote!
Explanation: The condition age >= 18 is true for age = 19, so the message is printed. If age were less than 18, nothing would happen.
Advanced Example: Password Strength Check
This example checks if a password length is sufficient for basic security.
#include <stdio.h>
#include <string.h>
int main() {
char password[50];
printf("Enter your password: ");
scanf("%s", password);
if (strlen(password) >= 8) {
printf("Password is long enough for basic security.\n");
}
printf("Program ends.\n");
return 0;
}
Output (if user enters "mysecretpass"):
Enter your password: mysecretpass
Password is long enough for basic security.
Program ends.
Output (if user enters "short"):
Enter your password: short
Program ends.
Explanation: The if statement checks if the password length (strlen(password)) is at least 8 characters. If true, it confirms the password’s length is sufficient. The program continues regardless, printing "Program ends."
2. if-else Statement
The if-else statement provides an alternative path when the if condition is false. It’s like choosing between coffee or tea based on availability.
Syntax:
if (condition) {
// Code if condition is true
} else {
// Code if condition is false
}
Basic Example: Check if a Number is Positive or Negative
#include <stdio.h>
int main() {
int num = -5;
if (num >= 0) {
printf("%d is positive or zero.\n", num);
} else {
printf("%d is negative.\n", num);
}
return 0;
}
Output:
-5 is negative.
Explanation: Since num is -5, the condition num >= 0 is false, so the else block executes.
Advanced Example: Temperature Alert System
This program checks if the temperature is safe for outdoor activities.
#include <stdio.h>
int main() {
float temp;
printf("Enter current temperature (Celsius): ");
scanf("%f", &temp);
if (temp >= 15 && temp <= 30) {
printf("Temperature %.1f°C is ideal for outdoor activities.\n", temp);
} else {
printf("Warning: Temperature %.1f°C is not ideal. Stay cautious!\n", temp);
}
return 0;
}
Output (if user enters 25):
Enter current temperature (Celsius): 25
Temperature 25.0°C is ideal for outdoor activities.
Output (if user enters 35):
Enter current temperature (Celsius): 35
Warning: Temperature 35.0°C is not ideal. Stay cautious!
3. Nested if-else Statement
Nested if-else statements allow you to check multiple conditions hierarchically, like a decision tree.
Syntax:
if (condition1) {
if (condition2) {
// Code if both are true
} else {
// Code if condition1 is true but condition2 is false
}
} else {
// Code if condition1 is false
}
Basic Example: Student Grade Check
#include <stdio.h>
int main() {
int score = 85;
if (score >= 60) {
if (score >= 80) {
printf("Excellent! You got an A.\n");
} else {
printf("Good job! You got a B.\n");
}
} else {
printf("You need to improve. Grade below B.\n");
}
return 0;
}
Output:
Excellent! You got an A.
Explanation: The outer if checks if score >= 60. Since it’s true, the inner if checks if score >= 80. Since 85 satisfies both, the program prints an A grade.
Advanced Example: Loan Eligibility System
This program determines loan eligibility based on credit score and income.
#include <stdio.h>
int main() {
int credit_score;
float annual_income;
printf("Enter your credit score (300-850): ");
scanf("%d", &credit_score);
printf("Enter your annual income ($): ");
scanf("%f", &annual_income);
if (credit_score >= 700) {
if (annual_income >= 50000) {
printf("Congratulations! You are eligible for a premium loan.\n");
} else {
printf("You qualify for a standard loan due to lower income.\n");
}
} else {
if (credit_score >= 600) {
printf("You may qualify for a limited loan.\n");
} else {
printf("Sorry, you are not eligible for a loan at this time.\n");
}
}
return 0;
}
Output (if user enters 750, 60000):
Enter your credit score (300-850): 750
Enter your annual income ($): 60000
Congratulations! You are eligible for a premium loan.
Output (if user enters 650, 40000):
Enter your credit score (300-850): 650
Enter your annual income ($): 40000
You may qualify for a limited loan.
Explanation: The outer if checks if credit_score >= 700. If true, it checks annual_income >= 50000 to decide between premium or standard loans. If the credit score is below 700, it checks if it’s at least 600 for a limited loan, otherwise denies eligibility.
4. Ladder if (else-if Ladder)
The else-if ladder checks multiple conditions sequentially, stopping at the first true condition. It’s like a flowchart with multiple branches.
Syntax:
if (condition1) {
// Code for condition1
} else if (condition2) {
// Code for condition2
} else if (condition3) {
// Code for condition3
} else {
// Code if no condition is true
}
Basic Example: Traffic Light System
#include <stdio.h>
int main() {
char color = 'R';
if (color == 'R') {
printf("Stop! Red light.\n");
} else if (color == 'Y') {
printf("Caution! Yellow light.\n");
} else if (color == 'G') {
printf("Go! Green light.\n");
} else {
printf("Invalid light color.\n");
}
return 0;
}
Output:
Stop! Red light.
Explanation: The program checks the value of color. Since it’s 'R', the first if block executes, and the rest are skipped.
Advanced Example: Restaurant Discount System
This program applies discounts based on the bill amount and customer type.
#include <stdio.h>
int main() {
float bill_amount;
char customer_type; // R = Regular, V = VIP, S = Student
printf("Enter bill amount ($): ");
scanf("%f", &bill_amount);
printf("Enter customer type (R for Regular, V for VIP, S for Student): ");
scanf(" %c", &customer_type);
float discount = 0;
if (bill_amount > 200 && customer_type == 'V') {
discount = bill_amount * 0.20; // 20% for VIPs over $200
printf("VIP Discount: $%.2f\n", discount);
} else if (bill_amount > 100 && customer_type == 'R') {
discount = bill_amount * 0.10; // 10% for Regulars over $100
printf("Regular Discount: $%.2f\n", discount);
} else if (bill_amount > 50 && customer_type == 'S') {
discount = bill_amount * 0.15; // 15% for Students over $50
printf("Student Discount: $%.2f\n", discount);
} else {
printf("No discount applicable.\n");
}
printf("Final bill after discount: $%.2f\n", bill_amount - discount);
return 0;
}
Output (if user enters 250, 'V'):
Enter bill amount ($): 250
Enter customer type (R for Regular, V for VIP, S for Student): V
VIP Discount: $50.00
Final bill after discount: $200.00
Output (if user enters 80, 'R'):
Enter bill amount ($): 80
Enter customer type (R for Regular, V for VIP, S for Student): R
No discount applicable.
Final bill after discount: $80.00
Explanation: The ladder checks conditions in order:
-
VIPs with bills over $200 get a 20% discount.
-
Regulars with bills over $100 get a 10% discount.
-
Students with bills over $50 get a 15% discount. If none apply, no discount is given. The final bill reflects the discount.
5. switch Case
The switch statement is ideal for selecting one option from multiple possible values of a variable, like choosing a menu item.
Syntax:
switch (expression) {
case value1:
// Code
break;
case value2:
// Code
break;
default:
// Code if no case matches
}
Basic Example: Month Name Display
#include <stdio.h>
int main() {
int month = 4;
switch (month) {
case 1:
printf("January\n");
break;
case 2:
printf("February\n");
break;
case 3:
printf("March\n");
break;
case 4:
printf("April\n");
break;
default:
printf("Invalid month\n");
}
return 0;
}
Output:
April
Explanation: The value of month (4) matches case 4, so "April" is printed. The break ensures the program exits the switch block.
Advanced Example: Calculator with Error Handling
This program creates a simple calculator using switch with input validation.
#include <stdio.h>
int main() {
float num1, num2, result;
char operator;
printf("Enter two numbers (e.g., 5 3): ");
scanf("%f %f", &num1, &num2);
printf("Enter operator (+, -, *, /): ");
scanf(" %c", &operator);
switch (operator) {
case '+':
result = num1 + num2;
printf("%.2f + %.2f = %.2f\n", num1, num2, result);
break;
case '-':
result = num1 - num2;
printf("%.2f - %.2f = %.2f\n", num1, num2, result);
break;
case '*':
result = num1 * num2;
printf("%.2f * %.2f = %.2f\n", num1, num2, result);
break;
case '/':
if (num2 != 0) {
result = num1 / num2;
printf("%.2f / %.2f = %.2f\n", num1, num2, result);
} else {
printf("Error: Division by zero is not allowed.\n");
}
break;
default:
printf("Error: Invalid operator.\n");
}
return 0;
}
Output (if user enters 10, 5, '+'):
Enter two numbers (e.g., 5 3): 10 5
Enter operator (+, -, *, /): +
10.00 + 5.00 = 15.00
Output (if user enters 8, 0, '/'):
Enter two numbers (e.g., 5 3): 8 0
Enter operator (+, -, *, /): /
Error: Division by zero is not allowed.
Explanation: The switch evaluates the operator. For +, -, *, it performs the calculation. For /, it checks for division by zero to avoid errors. The default case handles invalid operators. The %.2f format ensures two decimal places in output.
Why Decision-Making Statements Are Powerful
Decision-making statements let your program:
-
Respond dynamically to user inputs or data.
-
Handle complex logic with nested conditions or ladders.
-
Create user-friendly applications like calculators or eligibility systems.
Pro Tip: Combine these statements to build real-world projects, like:
-
A quiz app using switch for question selection.
-
A billing system with discounts using else-if ladders.
-
A game with nested conditions for player decisions.
Try tweaking these examples (e.g., add more cases to the calculator or new discount rules) to deepen your understanding. Happy coding!