Tips on how to Calculate the Sum of a Sequence in C

The problem

Your process is to make perform, which returns the sum of a sequence of integers.

The sequence is outlined by 3 non-negative values: start, finish, step (inclusive).

If start worth is larger than the finish, perform ought to returns ****

Examples

2,2,2 --> 2
2,6,2 --> 12 (2 + 4 + 6)
1,5,1 --> 15 (1 + 2 + 3 + 4 + 5)
1,5,3  --> 5 (1 + 4)

The answer in C

Choice 1:

unsigned sequence_sum(int begin, int finish, int step) {
    int sum=0,i;
    for(i=begin;i<=finish;i=i+step)
        sum=sum+i;
    return sum;
}

Choice 2:

unsigned sequence_sum(unsigned begin, unsigned finish, unsigned step) {
  if(begin > finish) return 0;
  else {
    unsigned n = (finish - begin)/step;
    return ((n + 1)*begin + n*(n + 1)*step/2);
  }
}

Choice 3:

unsigned sequence_sum(unsigned begin, unsigned finish, unsigned step){
  if(begin > finish) return 0;
  int n = (end-start)/step + 1;
  return (n)*(2*begin+(n-1)*step)/2;
}

Take a look at circumstances to validate our resolution

#embrace <criterion/criterion.h>

unsigned sequence_sum(unsigned begin, unsigned finish, unsigned step);

Take a look at(Sample_Test, should_return_the_sum_of_sequence)
{
    cr_assert_eq(sequence_sum(2u, 6u, 2u), 12u);
    cr_assert_eq(sequence_sum(1u, 5u, 1u), 15u);
    cr_assert_eq(sequence_sum(1u, 5u, 3u), 5u);
    cr_assert_eq(sequence_sum(0u, 15u, 3u), 45u);
    cr_assert_eq(sequence_sum(16u, 15u, 3u), 0u);
}