Difference between fork() and exec()

// C program to illustrate use of fork() &
// exec() system call for process creation

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h> 
#include <stdlib.h>
#include <errno.h> 
#include <sys/wait.h>

int main(){
pid_t pid;
int ret = 1;
int status;
pid = fork();

if (pid == -1){

    // pid == -1 means error occurred
    printf("can't fork, error occurred\n");
    exit(EXIT_FAILURE);
}
else if (pid == 0){

    // pid == 0 means child process created
    // getpid() returns process id of calling process
    // Here It will return process id of child process
    printf("child process, pid = %u\n",getpid());
    // Here It will return Parent of child Process means Parent process it self
    printf("parent of child process, pid = %u\n",getppid()); 

    // the argv list first argument should point to 
    // filename associated with file being executed
    // the array pointer must be terminated by NULL 
    // pointer
    char * argv_list[] = {"ls","-lart","/home",NULL};

    // the execv() only return if error occurred.
    // The return value is -1
    execv("ls",argv_list);
    exit(0);
}
else{
    // a positive number is returned for the pid of
    // parent process
    // getppid() returns process id of parent of 
    // calling process
// Here It will return parent of parent process's ID
    printf("Parent Of parent process, pid = %u\n",getppid());
    printf("parent process, pid = %u\n",getpid()); 

        // the parent process calls waitpid() on the child
        // waitpid() system call suspends execution of 
        // calling process until a child specified by pid
        // argument has changed state
        // see wait() man page for all the flags or options
        // used here 
        if (waitpid(pid, &status, 0) > 0) {
            
            if (WIFEXITED(status) && !WEXITSTATUS(status)) 
            printf("program execution successful\n");
            
            else if (WIFEXITED(status) && WEXITSTATUS(status)) {
                if (WEXITSTATUS(status) == 127) {

                    // execv failed
                    printf("execv failed\n");
                }
                else
                    printf("program terminated normally,"
                    " but returned a non-zero status\n");             
            }
            else
            printf("program didn't terminate normally\n");         
        } 
        else {
        // waitpid() failed
        printf("waitpid() failed\n");
        }
    exit(0);
}
return 0;
}