Small and simple code snippet for measuring CPU time (both user and system) in C:

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// tik.h
#include <stdio.h>
#include <time.h>
void tik()
{
    static clock_t start, end;
    static int flag = 0;
    static double elapsed_time;
    if (flag == 0) {
        start = clock();
    } else {
        end = clock();
        elapsed_time = (double)(end - start) / (double)CLOCKS_PER_SEC;
        printf("%f\n", elapsed_time);
        // printf("Elapsed time: %f seconds\n", elapsed_time);
    }
    flag = 1 - flag;
}

Usage:

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#include "./tik.h"
int main(int argc, char **argv)
{
    tik();
    int count = 1 << 25;
    for (int i = 0; i < count; ++i) ;
    tik();
}