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Creating a program in C to calculate simple interests is a fundamental exercise for beginners and intermediate programmers. This tutorial will guide you through the process, including examples and explanations, to help you understand and build this practical program.

What is Simple Interest?

Simple interest is a way of calculating the interest on a loan or investment. It is calculated by multiplying the principal amount (the initial amount borrowed or invested) by the interest rate and the time period. This is a standard method for short-term loans and investments.

Algorithm to Calculate Simple Interest

  1. Initialize Variables: Declare variables to store the principal amount (P), interest rate (R), time period (T), and simple interest (SI).
  2. Input Values: Prompt the user to enter the principal amount, interest rate, and time period. Use the scanf() function to take input from the user.
  3. Calculate Interest: Apply the simple interest formula: SI = (P * R * T) / 100. This formula calculates the simple interest based on the provided principal amount, interest rate, and time period.
  4. Output Result: Display the calculated simple interest using the printf() function. Format the output using %.2f to display two decimal places.

Code Example

Here's a C program that calculates simple interest using the above algorithm:

#include <stdio.h>

int main() {
    float principal, rate, time, interest;

    // Take user input for principal, rate, and time
    printf("Enter principal amount: ");
    scanf("%f", &principal);
    printf("Enter interest rate: ");
    scanf("%f", &rate);
    printf("Enter time period (in years): ");
    scanf("%f", &time);

    // Calculate simple interest
    interest = (principal * rate * time) / 100;

    // Display the result
    printf("Simple Interest is: %.2f\n", interest);

    return 0;

Program Output:

For example, if you input a principal amount of 1000, an interest rate of 6%, and a time period of 2 years, the program will calculate and display the simple interest as 120.00.

Enter principal amount: 1000
Enter interest rate: 6
Enter time period (in years): 2
Simple Interest is: 120.00


Writing a C program to calculate simple interest is a straightforward process. By understanding the concept of simple interest and following the provided algorithm, you can easily create a program to perform these calculations.

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