Sum of AP series

A series with same common difference is known as arithmetic series. The first term of series is 'a' and common difference is d. The series looks like a, a d, a 2d, a 3d, . . . Find the sum of series.A series with the same common difference is called an arithmetic series. The first term in the series is "a" and the common difference is d. The series looks like a d, a 2d, a 3d... Find the sum of the series.

<strong>Input :</strong> a = 1
        d = 2
        n = 4
<strong>Output :</strong> 16
+ 3 + 5 + 7 = 16

<strong>Input :</strong> a = 2.5
        d = 1.5
        n = 20
<strong>Output :</strong> 335

Input:
The first line consists of an integer T i.e number of test cases. The first line and only line of each test case consists of three integers a,d,n.

enter:
The first line consists of the integer T, which is the number of test cases. The first and first lines of each test case consist of three integers a, d, n.

Output:
Print the sum of the series. With two decimal places.

Output:
Print the sum of the series. There are two decimal places.

Constraints:
1 1

constraint:
1 1
Example:

Input:
1 2 4
2.5 1.5 20

<strong>Output:</strong>
16.00
335.00

In fact, it is a summation problem of an arithmetic sequence, but it should be noted that the output is two decimal places.

The following is my code implementation:

#include 
#include 

int main()
{
    int n,i,j;
    scanf("%d",&n);
    for(i=0;i<n float a scanf printf return>
<p>Then an error occurred? Let’s take a look: </p>
<p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/164/171029420168387.png" class="lazy" alt="Sum of AP series">I tried the double type several times, but the same error occurred. Don’t quite understand how to do it? Where is the inspection point for this question? </p></n>

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