Shell Program in C, running executable in background - shell

Question

I am writing a simple shell program in C and I believe I have it just about finished. The program should continually print "Prompt>" and wait for a user to either enter the name of an executable along with any parameters the executable needs. The shell only has one built in function, quit, which ends the program. If the user were to put an '&' at the end of the line then the given executable should be run in the background. (Built-in functions and commands without the '&' should run in the foreground and wait for the child process to finish.) However when I run my code and put an '&' at the end of my line, the executable runs and finishes but I no longer see the "prompt>" show up. I can still enter the name of an executable or quit and it runs and everything but I don't understand why the prompt isn't showing up.
Also as a side question. Is my program properly handling child processes? Basically, am I not leaving zombie processes with this code?
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>
#include <string.h>
#define MAXBUFF 100
#define MAXLINE 200
int parse_line(char *buffer, char **arg_array);
void evaluate_commandline(char *commandline);
int builtin_command();
int parse_line(char *buffer, char **arg_array){
char *delimiter;
int num_args;
int run_background;
buffer[strlen(buffer)-1] = ' ';
while(*buffer && (*buffer == ' '))
buffer++;
num_args = 0;
while((delimiter = strchr(buffer, ' '))){
arg_array[num_args++] = buffer;
*delimiter = '\0';
buffer = delimiter + 1;
while(*buffer && (*buffer == ' '))
buffer++;
}
arg_array[num_args] = NULL;
if(num_args == 0)
return 1;
if((run_background = (*arg_array[num_args-1] == '&')) != 0)
arg_array[--num_args] = NULL;
return run_background;
}
void evaluate_commandline(char *commandline){
char *arg_array[MAXBUFF];
char buffer[MAXLINE];
int run_background;
pid_t pid;
strcpy(buffer, commandline);
run_background = parse_line(buffer, arg_array);
if(arg_array[0] == NULL)
return;
if(!builtin_command(arg_array)){
if((pid = fork())== 0){
if(execvp(arg_array[0],arg_array)< 0){
printf("%s: Command not found.\n", arg_array[0]);
exit(0);
}
}
if(!run_background){
int child_status;
wait(&child_status);
}
}
return;
}
int builtin_command(char **arg_array){
if(!strcmp(arg_array[0],"quit"))
exit(0);
return 0;
}
int main(){
char commandline[MAXLINE];
while(1){
printf("prompt> ");
fgets(commandline, MAXLINE, stdin);
if(feof(stdin))
exit(0);
evaluate_commandline(commandline);
}
}

Answer 1

i think where you say:
if(!run_background){
you forget a "else"
else if(!run_background){