Summing a list of values, with for loop in C

Question

New to C and I need some guidance. I understand why the my code is outputting "55" instead of "40"; but I have no idea how to fix this. Any advice? Some of the variables listed are obsolete, and were simply put in to experiment with. Just to clarify, lower/upper are just the min/max values for the range.

#include<stdio.h>
#include<stdlib.h>

int sum = 0;
int main() {
    int n = 10;
    int m = 2;
    int i, x;
    int upper;
    int lower;
    int lower1[100];
    int upper1[100];
    int sum_p =0;

    for (i = 1; i <= m; i++) {
        lower = 1 + (i - 1) * (n / m);
        lower1[i] = lower;
        upper = i * (n / m);
        upper1[i] = upper;

        if (i == m) {
            upper = n;
            upper1[i] = upper;
        }
        else {
            upper = i * (n / m);
            upper1[i] = upper;
        }
    }

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

   printf("The total sum is: %d\n",sum);

   for (i = 1; i <= m; i++) {
       printf("Range is %d to %d\n", lower1[i], upper1[i]);

       for(x = lower1[i]; x <= upper1[i]; ++x)
           sum_p += x;

       printf("Sum:%d\n",sum_p);
   }
}

This code outputs:

The total sum is: 55
Range is 1 to 5
Sum:15
Range is 6 to 10
Sum:55

My desired output is:

The total sum is: 55
Range is 1 to 5
Sum: 15
Range is 6 to 10 /*6+7+8+9+10*/
Sum: 40

Answer 1

sum_p is not reset to zero between cases.