very unoptimized way of calculating the cpu usage percentage

cpu_usage.c

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

struct cpu_data_t {
  int user, nice, system, idle, iowait, irq, softirq, steal, guest, guest_nice;
};

// based on answer here: https://stackoverflow.com/a/23376195/8295404
float calculate_cpu_percentage(struct cpu_data_t prev, struct cpu_data_t curr) {
  float PrevIdle = prev.idle + prev.iowait;
  float Idle = curr.idle + curr.iowait;

  float PrevNonIdle = prev.user + prev.nice + prev.system + prev.irq +
                      prev.softirq + prev.steal;
  float NonIdle = curr.user + curr.nice + curr.system + curr.irq +
                  curr.softirq + curr.steal;

  float PrevTotal = PrevIdle + PrevNonIdle;
  float Total = Idle + NonIdle;

  float totald = Total - PrevTotal;
  float idled = Idle - PrevIdle;

  return (totald - idled) / totald;
}

struct cpu_data_t get_cpu_data() {
  struct cpu_data_t cpu_data;
  FILE *fp;
  char *line = NULL;
  size_t len = 0;
  fp = fopen("/proc/stat", "r");
  if (fp == NULL) {
    exit(EXIT_FAILURE);
  }

  while (getline(&line, &len, fp) != -1) {
    char *pch = strtok(line, " ,.-");
    int value = strcmp("cpu", pch);
    if (value == 0) {
      pch = strtok(NULL, " ,.-");
      for (int i = 0; i < 10; ++i) {
        if (i == 0) {
          cpu_data.user = atof(pch);
        }
        if (i == 1) {
          cpu_data.nice = atof(pch);
        }
        if (i == 2) {
          cpu_data.system = atof(pch);
        }
        if (i == 3) {
          cpu_data.idle = atof(pch);
        }
        if (i == 4) {
          cpu_data.iowait = atof(pch);
        }
        if (i == 5) {
          cpu_data.irq = atof(pch);
        }
        if (i == 6) {
          cpu_data.softirq = atof(pch);
        }
        if (i == 7) {
          cpu_data.steal = atof(pch);
        }
        if (i == 8) {
          cpu_data.guest = atof(pch);
        }
        if (i == 9) {
          cpu_data.guest_nice = atof(pch);
        }
        //   printf("%s\n", pch);
        pch = strtok(NULL, " ,.-");
      }
    }
  }

  fclose(fp);
  if (line) {
    free(line);
  }
  return cpu_data;
}

int main(void) {
  struct cpu_data_t prev, curr;
  prev = get_cpu_data();
  usleep(1100000);
  curr = get_cpu_data();
  while (1) {
    float cpu_percentage = calculate_cpu_percentage(prev, curr);
    printf("current cpu usage: %f\n", cpu_percentage * 100);
    prev = get_cpu_data();
    usleep(1100000);
    curr = get_cpu_data();
  }

  exit(EXIT_SUCCESS);
}