# C Program to find Sum of Geometric Progression Series

Write a C Program to find Sum of Geometric Progression Series (G.P. Series) using Math Formula, and without using Mathematical formula.

## Geometric Progression Series

Geometric Series is a sequence of terms in where the next element obtained by multiplying common ration to the previous element. Or G.P. Series is a series of numbers in which a common ratio of any consecutive numbers (items) is always the same.

The mathematical formula behind this Sum of G.P Series
Sn = a(rn) / (1- r)
Tn = ar(n-1)

## C Program to find Sum of Geometric Progression Series Example

It allows the user to enter the first value, the total number of items in a series, and the common ratio. Next, it will find the sum of the Geometric Progression Series. Here, we used For Loop to display the G.P series, which is optional.

```/* C Program to find Sum of Geometric Progression Series */
#include <stdio.h>
#include<math.h>
int main() {

int a, n, r;
float tn, sum = 0;

printf(" Please Enter First Number of an G.P Series:  ");
scanf("%d", &a);
printf(" Please Enter the Total Numbers in this G.P Series:  ");
scanf("%d", &n);
printf(" Please Enter the Common Ratio:  ");
scanf("%d", &r);

sum = (a * (1 - pow(r, n ))) / (1- r);
tn = a * (pow(r, n - 1));

printf("\n The Sum of Geometric Progression Series =  %.2f", sum);
printf("\n The tn Term of Geometric Progression Series = %.2f \n", tn);
return 0;
}```
`````` Please Enter First Number of an G.P Series:  1
Please Enter the Total Numbers in this G.P Series:  5
Please Enter the Common Ratio:  2

The Sum of Geometric Progression Series =  31.00
The tn Term of Geometric Progression Series = 16.00 ``````

In this Program, we are not using any Mathematical formula.

```/* C Program to find Sum of Geometric Progression Series */
#include <stdio.h>
#include<math.h>
int main() {

int a, n, r, value, i;
float sum = 0;

printf(" Please Enter First Number of an G.P Series:  ");
scanf("%d", &a);
printf(" Please Enter the Total Numbers in this G.P Series:  ");
scanf("%d", &n);
printf(" Please Enter the Common Ratio:  ");
scanf("%d", &r);

value = a;
printf("G.P Series  :  ");
for(i = 0; i < n; i++)
{
printf("%d  ", value);
sum = sum + value;
value = value * r;
}
printf("\n The Sum of Geometric Progression Series =  %f\n", sum);
return 0;
}```
`````` Please Enter First Number of an G.P Series:  2
Please Enter the Total Numbers in this G.P Series:  5
Please Enter the Common Ratio:  2
G.P Series  :  2  4  8  16  32
The Sum of Geometric Progression Series =  62.000000``````

## C Program to calculate Sum of Geometric Progression Series using Functions

This geometric progression C Program is same as above. However, we separated the C Programming logic using Functions

```/* C Program to find Sum of Geometric Progression Series */
#include <stdio.h>
#include<math.h>
int sumofGP(int a, int n, int r)
{
int sum = (a * (1 - pow(r, n))) / (1- r);
return sum;
}

int main() {

int a, n, r;
float sum = 0;

printf(" Please Enter First Number of an G.P Series:  ");
scanf("%d", &a);
printf(" Please Enter the Total Numbers in this G.P Series:  ");
scanf("%d", &n);
printf(" Please Enter the Common Ratio:  ");
scanf("%d", &r);

sum = sumofGP(a, n, r);
printf("\n The Sum of Geometric Progression Series =  %f\n", sum);
return 0;
}```