# C Exercises: Display the sum of the series [ 9 + 99 + 999 + 9999 ...]

## C For Loop: Exercise-21 with Solution

Write a program in C to display the sum of the series [ 9 + 99 + 999 + 9999 ...].

This C program calculates and displays the sum of a series where each term is formed by repeating the digit 9 (e.g., 9, 99, 999, 9999, ...). The program prompts the user for the number of terms (n) and then computes the sum using a loop that generates each term and adds it to the total sum. The final sum is then printed to the console.

**Visual Presentation:**

**Sample Solution:**

**C Code:**

```
#include <stdio.h> // Include the standard input/output header file.
void main()
{
long int n, i, t = 9; // Declare variables to store input, control loop indices, and temporary value.
int sum = 0; // Initialize a variable to store the sum.
printf("Input the number or terms :"); // Prompt the user for input.
scanf("%ld", &n); // Read the value of 'n' from the user.
for (i = 1; i <= n; i++) // Loop for the number of terms.
{
sum += t; // Add 't' to the sum.
printf("%ld ", t); // Print the current value of 't'.
t = t * 10 + 9; // Update 't' for the next iteration.
}
printf("\nThe sum of the series = %d \n", sum); // Print the sum of the series.
}
```

Output:

Input the number or terms :5 9 99 999 9999 99999 The sum of the series = 111105

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