Q:

# C program to calculate sum of the series 1 + 11 + 111 + 1111 + ... N terms

To find (calculate) the sum of series 1+11+111+1111+... till N terms using C program - we are reading total number of terms by the user and using following steps:

• Declared variables to stores sum of the values (sum), loop counter (i) and a variable to store term (temp) value (like, 1, 11, 111,.. )
• Assigning 0 to the variable sum and initial value 1 to the temp
• Within the loop - first we are adding the temp value to the sum and them increasing the value of temp to make it next term value.
• And, after the loop – we are printing the value of the sum.

## Program to calculate sum of series 1+11+111+1111+... till N terms in C

``````#include <stdio.h>

int main()
{
int terms; //to store total terms
int i; //to run loo;
long int sum; //to store sum of values
long int temp; //to add the diff or initial term value

//assign 0 to sum and assign 1 as initial term value
sum =0;
temp =1;

//input total terms
printf("Enter total number of terms: ");
scanf("%d",&terms);

//run loop to find sum of each value
//and then increase it with the differences
for(i=0; i<terms; i++)
{
//print the  value
printf("%ld ", temp);
if(i<terms-1)
printf("+ ");

//add the value and store in sum
sum += temp;
//update/increase the value
temp = (temp*10)+1;
}

//print the value of sum of the series
printf("\nSUM of the series is: %ld\n",sum);

return 0;
}``````

Output

```First run:
Enter total number of terms: 5
1 + 11 + 111 + 1111 + 11111
SUM of the series is: 12345

Second run:
Enter total number of terms: 10
1 + 11 + 111 + 1111 + 11111 + 111111 + 1111111 + 11111111 + 111111111 + 1111111111
SUM of the series is: 1234567900```