Проблема с компиляцией под Ubuntu

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <iostream>
#include <math.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>
#include <cstring>
#include <fcntl.h>
 
struct tms {
    clock_t tms_utime; /* user time */
    clock_t tms_stime; /* system time */
    clock_t tms_cutime; /* user time of children */
    clock_t tms_cstime; /* system time of children */
};
clock_t times(struct tms *buf);
 
int main(void){
    int i=0, fork1=0, ut=0, st, cu, cs, status;
    double res;
    FILE *fOut;
    struct tms start_time, end_time;
    clock_t real_time;
    fOut = fopen("text1.txt", "w");
    real_time = times(& start_time);
    for(i = 0; i < 500000; i++){
        res = i*3 + sin(i) - sqrt(i/15);
        fprintf(fOut, "%e, ", res);
    }
    for(i=0;i<3;i++){
        fork1 = fork();
        if(fork1 == 0){
            execl("./son21", "son21", NULL);
            execl("./son21", "son21", NULL);
        }
        else{
            wait(&status);
        }
        if(fork1 == -1){
            printf("Father: Error fork:\n %s", strerror(errno));
        }
    };
    if(fork1!=0){
        execl("./son12", "son12", NULL);
    }
    real_time = times(&end_time);
    ut = end_time.tms_utime - start_time.tms_utime;
    st = end_time.tms_stime - start_time.tms_stime;
    cu = end_time.tms_cutime - start_time.tms_cutime;
    cs = end_time.tms_cstime - start_time.tms_cstime;
    printf("fatherPid=%d,ppid=%d,ut=%d,st=%d,cu=%d,cs=%d\n", getpid(), getppid(), ut, st, cu, cs);
    fclose(fOut);
    exit(0);
}

#include <sys/times.h>

#include <sys/time.h>