====== Compute execution time of a C program ======

Normal usage:
<code c execution-time.c>
#include <sys/time.h>
#include <stdio.h>

struct timeval start, end;

// Start the timer
gettimeofday(&start, NULL);

// Here is the code to be executed

// End the timer
gettimeofday(&end, NULL);

// Calculating the time difference in seconds and microseconds
long seconds = end.tv_sec - start.tv_sec;
long micros = ((seconds * 1000000) + end.tv_usec) - (start.tv_usec);

// Convert time to seconds and print
double time_in_seconds = seconds + micros / 1000000.0;
printf("Time elapsed: %ld microseconds (%.6f seconds)\n", micros, time_in_seconds);

</code>

Concrete example - Bubble Sort:

<code c bubble-sort-exec-time.c>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

#define ARRAY_SIZE 10000

void bubbleSort(int arr[], int n) {
    int i, j, temp;
    for (i = 0; i < n - 1; i++) {
        for (j = 0; j < n - i - 1; j++) {
            if (arr[j] > arr[j + 1]) {
                temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
}

void fillArray(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        arr[i] = rand() % 1000;  // Random numbers between 0 and 999
    }
}

void printArray(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int arr[ARRAY_SIZE];
    struct timeval start, end;

    fillArray(arr, ARRAY_SIZE);

    // Start the timer
    gettimeofday(&start, NULL);

    // Execute the sorting algorithm
    bubbleSort(arr, ARRAY_SIZE);

    // End the timer
    gettimeofday(&end, NULL);

    // Calculating the time difference in seconds and microseconds
    long seconds = end.tv_sec - start.tv_sec;
    long micros = ((seconds * 1000000) + end.tv_usec) - (start.tv_usec);

    // Convert time to seconds and print
    double time_in_seconds = seconds + micros / 1000000.0;
    printf("Time elapsed: %ld microseconds (%.6f seconds)\n", micros, time_in_seconds);

    // Optional: Print sorted array
    // printArray(arr, ARRAY_SIZE);

    return 0;
}
</code>