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;
}

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;
}

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;
}