Examples of C part 63 to find the sum of series in arithmetic expression

Program :

#include<stdio.h>
main()
{
//an=a+(n-1)d
//lastnum=num1+(n-1)diff  this is formula from our variables
//n=((an-a)/d)+1
  int i,n,sum=0,num1,num2,diff,lastnum,series;

  printf("Enter first 2 numbers for finding common Difference\n");
  scanf("%d%d",&num1,&num2);
  printf("Enter last term of series\n");
  scanf("%d",&lastnum);
  diff=num2-num1;
  series=num1;

  n=((lastnum-num1)/diff)+1;
  printf("Number of terms in series is %d\n",n);

  for(i=1;i<=n;i++)
  {
   sum+=series;
   series+=diff;
  }

  series=num1;
  printf("Sum of the series\n");
    for(i=1;i<=n;i++)
  {
     if(i<n)
     {
      printf("%d+",series);
      series+=diff;
     }
     else
     {
      printf("%d=%d\n",series,sum);
      series+=diff;
     }
  }
}

Output:
Enter first 2 numbers for finding common Difference
1
5
Enter last term of series
53
Number of terms in series is 14
Sum of the series
1+5+9+13+17+21+25+29+33+37+41+45+49+53=378
Explanation:
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