Why is the elapsed time 0?

Question

I made a program that unrolls loops and measures the time taken for it to sort an array, but the problem I have is that sometimes the unrolled loop program gives me an answer of 0 in nano seconds and that just can't be. I tried it with MONOTONIC too but just doesn't help. Here's my code:

    #include <stdio.h>
    #include <time.h>
    #include <stdlib.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <math.h>
    #include <unistd.h>
    #define BILLION  1000000000L
    int main()
    {
        char buf[500];
        int numberOfElements = 10;
        int currentTest = 1;
        int randomArray[numberOfElements];
        int minIndex;
        int minValue;
        struct timespec requestStart;
        struct timespec requestEnd;
        long int recordStartTime;
        long int recordEndTime;
        long int elapsedTime;
        FILE *arrangedArray;
        FILE *stopwatch;
        sprintf(buf,"place to store file/Stopwatch.txt", currentTest);
        stopwatch = fopen(buf, "a+");
        struct stat st = {0};
        sprintf(buf, "the place where you stored the stopwatch file", currentTest);
        if (stat(buf, &st) == -1)
        {
            sprintf(buf, "the place where you stored the stopwatch file", currentTest);
            mkdir(buf);
        }
        sprintf(buf, "the place where you store this program/ArrangedArray.txt", currentTest);
        arrangedArray = fopen(buf, "w+");
        randomArray[0] = 7045;

        randomArray[1] = 4949;

        randomArray[2] = 24507;

        randomArray[3] = 6071;

        randomArray[4] = 11820;

        randomArray[5] = 11710;

        randomArray[6] = 11168;

        randomArray[7] = 11234;

        randomArray[8] = 11863;

        randomArray[9] = 2683;

        clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &requestStart);
        recordStartTime = requestStart.tv_nsec + requestStart.tv_sec * BILLION;
        minIndex = 0;

        minIndex = 1;

        minIndex = 9;

        minValue = randomArray[9];

        randomArray[9] = randomArray[0];

        randomArray[0] = 2683;

        minIndex = 1;

        minIndex = 2;

        minIndex = 3;

        minValue = randomArray[3];

        randomArray[3] = randomArray[2];

        randomArray[2] = 6071;

        minIndex = 3;

        minIndex = 4;

        minIndex = 5;

        minIndex = 6;

        minIndex = 9;

        minValue = randomArray[9];

        randomArray[9] = randomArray[3];

        randomArray[3] = 7045;

        minIndex = 4;

        minIndex = 5;

        minIndex = 6;

        minValue = randomArray[6];

        randomArray[6] = randomArray[4];

        randomArray[4] = 11168;

        minIndex = 5;

        minIndex = 7;

        minValue = randomArray[7];

        randomArray[7] = randomArray[5];

        randomArray[5] = 11234;

        minIndex = 6;

        minIndex = 7;

        minValue = randomArray[7];

        randomArray[7] = randomArray[6];

        randomArray[6] = 11710;

        minIndex = 7;

        minIndex = 8;

        minIndex = 9;

        clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &requestEnd);
        recordEndTime = (requestEnd.tv_nsec + requestEnd.tv_sec * BILLION);
        elapsedTime = recordEndTime - recordStartTime;
        sprintf(buf, "%li\n", elapsedTime);
        fputs(buf, stopwatch);
        sprintf(buf, "%i\n", randomArray[0]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[1]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[2]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[3]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[4]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[5]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[6]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[7]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[8]);
        fputs(buf, arrangedArray);
        sprintf(buf, "%i\n", randomArray[9]);
        fputs(buf, arrangedArray);

        fclose(arrangedArray);
        fclose(stopwatch);
        return 0;
    }