# C program to calculate compound interest

In this post, you will learn how to calculate the **compound interest** using the **C** programming language.

Compound interest is the addition of interest to the principal sum of a loan or deposit, or in other words, interest on interest. Compound interest makes a sum of money grow at a faster rate than simple interest because in addition to earning returns on the money you invest, you also earn returns on those returns at the end of every compounding period.

## Compound Interest Formula

The **Compound Interest (C.I.)** formula is calculated as -

`Compound Interest = P(1 + R/100)`^{r}
Where,
P is the principle amount
T is the time and
R is the rate

## C program to calculate Compound Interest

In the given C program, we allow users to enter the principal amount, rate of interest, and number of years. By using these values, the program calculates compound interest.

```
#include <stdio.h>
#include <math.h>
int main()
{
float p, r, t, CI;
// Input principle, time and rate
printf("Enter the principal amount : ");
scanf("%f", &p);
printf("Enter the time span : ");
scanf("%f", &t);
printf("Enter rate of interest : ");
scanf("%f", &r);
// Calculate compound interest
CI = p* (pow((1 + r / 100), t));
printf("Compound Interest = %f", CI);
return 0;
}
```

**Output 1 -**

```
Enter the principal amount : 34000
Enter the time span : 5
Enter rate of interest : 6.5
Compound Interest = 46582.960938
```

**Output 2 -**

```
Enter the principal amount : 42000
Enter the time span : 8
Enter rate of interest : 7.5
Compound Interest = 74906.093750
```

## C program to calculate Compound Interest using function

In the given C program, we define a user function to calculate the compound interest.

```
#include<stdio.h>
#include<math.h>
float compound_interest(float P, float T, float R) {
return P*(pow(1+(R/100), T));
}
int main() {
float p, t, r;
printf("Enter Principle amount, rate of interest, and time: ");
scanf("%f%f%f", &p, &r, &t);
printf("Interest value: %f", compound_interest(p, t, r));
}
```

**Output of the above code:**

```
Enter Principle amount, rate of interest, and time: 12000 4.7 5
Interest value: 15097.837891
```

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