executing commands in own shell - C -

i have troubles creating own shell in c. here code have far

#include "interpreter.h"  #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/wait.h> #include <syslog.h>    void readconfig(int *timeout, char *file){     file * fp;     char * line = null;     size_t len = 0;     char * token;     fp = fopen(config, "r");     if (fp == null)     {          *timeout = defaulttime;      }     else     {         while ((getline(&line, &len, fp)) != -1){             token = strtok(line, token);             if ((strcmp(token,time_period) == 0)){                 *timeout = atoi(strtok(null, token));             }             if ((strcmp(token,history)==0)){                 strcpy(file,trim_command(strtok(null, token)));                          }         }     } }   int waitperiod(pid_t pid){     if(pid) {      int stat_val; pid_t child_pid;     int time = 0;      while(time < time_period){         child_pid = waitpid(pid, &stat_val, wnohang);              if (child_pid == pid){             break;             } else if (child_pid == 0) {                 time++;                 sleep(1);             }         }          if (time == time_period){             printf("process ended. execution time over. \n");             kill(pid, sigint);             if (kill(pid, 0) == 0){                 kill(pid, sigkill);             }         }                         if(wifexited(stat_val)) {             return wexitstatus(stat_val);         }          return 0;     } else {         return -1;     } }  void splitcommand(char ** parameters, char * command, int count){     char * cm = strtok(command, " ");     int = 0;     while (cm != null){              parameters[i] = malloc(strlen(cm) * sizeof(char *));         parameters[i] = cm;         i++;         cm = strtok (null, " ");     }            i++;     parameters[i] = null; }  int getparamscount(char command[]){     int i;     int count = 1;     int com_length = strlen(command);     for(i=0; i<com_length; i++){         if (command[i] == ' '){             count++;         }     }     return count; }  void gethistory(file * history_file, char ** history_commands){      char line[max_input];     int = 0;     int j;     rewind(history_file);     while (fgets(line, max_input, history_file)!= null){         history_commands[i] = malloc(strlen(line) * sizeof(char *));                 history_commands[i] = strdup(line);         for(j=0; j<max_input; j++){             if (history_commands[i][j] == '\n'){                 history_commands[i][j] = '\0';                 break;             }         }         i++;     } }  int getnumberofrows(file * history_file){     rewind(history_file);     int lines = 0;     char ch;     while(!feof(history_file)){         ch = fgetc(history_file);         if(ch == '\n'){             lines++;         }     }     return lines; }  void printcommands(char ** history_commands, int lines){     int = 0;     int j = 0;       for(j = i; j < lines; j++){         printf("[%d] %s\n", j, history_commands[j]);     } }  int runcommand(pid_t pid, char * command, char ** parameters, int child){     int count = 0;      switch(pid) {         case -1 :             return -1;         case 0 :             count = getparamscount(command);             parameters = malloc((count+1) * sizeof(char *));             splitcommand(parameters, command, count);             if (strncmp("cd", parameters[0], 2) == 0){                 chdir(parameters[1]);             } else {                 execvp(parameters[0], parameters[0]);             }             free(parameters);             return 0;         default :             child = waitperiod(pid);             printf("child status: %d\n", child);             command[0] = 0;             free(command);                       return 0;     } }  char * trim_command(char * string){     int l = strlen(string);     int i;     (i = 0; i<l; i++){         if (string[i] == '\n'){             string[i] = '\0';         }     }      return string; }    int main(){       char * command;      file * history;      char cwd[max_input];      pid_t pid = 0;       int child = 0;        int number_of_rows = 0;     int count = 0;      char ** history_commands;        char ** parameters[10];      printf("                              safe comand line interpreter                         \n");     printf("                    type \"quit\" cancel interpreter or command                  \n");     printf("                    type \"history\" show full command history                  \n");     printf("                    type \"history number\" execute command history       \n");     printf("________________________________________________________________________________________\n");     sleep(1);      history = fopen(history, "a+");     if (history == null){         printf("could not open history file\n");         return -1;     }      while(1){         getcwd(cwd, sizeof(cwd));         printf("command: [%d]%s : ", child, cwd);          command = malloc(max_input * sizeof(char *));         fgets(command, max_input, stdin);         trim_command(command);          if (strncmp(quit, command, 4) == 0) {             fclose(history);             return exit_success;         } else if (strncmp("history", command, 7) == 0) {                                                                    number_of_rows = getnumberofrows(history);                                                           history_commands = malloc(number_of_rows * sizeof(char *));                                  gethistory(history, history_commands);             count = getparamscount(command);                  if (strcmp("history", command) == 0){                     printf("history of commands\n");                     printcommands(history_commands, number_of_rows);                 } else {                     char * cm = strtok(command, " ");                     cm = strtok(null, " ");                      int x;                     x = atoi(cm);                      if (x >= number_of_rows){                         printf("command not exist\n");                         continue;                     }                      command = strdup(history_commands[x]);                     count = getparamscount(command);                     trim_command(command);                      fprintf(history, "%s\n", command);                      pid = fork();                     runcommand(pid, command, parameters, child);                 }           } else if (command[0] != 0){             fprintf(history, "%s\n", command);              pid = fork();             runcommand(pid, command, parameters, child);                     }     }      fclose(history);     return 0; } 

the problem is, doesn't execute cd command. when comment malloc , free lines in runcommand method, cd command starts working, every other command without parameter not working... me this?