Exit code 11 - how to fix it

Question

In the program below, I'm getting exit code 11. What I'm trying to do is to add a command "RUN filename". This command will take filename.txt and parse it to execute the commands in the file. So I intend to use fgets(). Also, in order to differentiate commands from the shell and from the file, I used a global boolean variable fromfile.

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>

// maximum number of registers
#define RMAX 4

// maximum length of a string
#define SMAX 80

// maximum number of memory locations
#define MMAX 16

// registers
int r[RMAX];

// memory
int m[MMAX];

// loop variable
int i;

// cmd input string
char cmd_input[SMAX];

// cmd portion of input (1st word)
char cmd[SMAX];

// argument portion of input (2nd word)
char arg[SMAX];
int iarg;                     // interger version of argument

// number words found in input
int wordsFound;

// display mode
char display_mode[4] = "DEC"; // same as {'D','E','C','\0'}

bool done = false;

FILE* fp = NULL;              // file pointer for basic input/output
FILE* runfp = NULL;           // file pointer for run file command

bool fromfile = false;

int temp;                     // temporary integer

void printRegister(int reg) {
    // prints value of r[reg] in correct display mode
    printf("[%s] ", display_mode);

    if (strcmp(display_mode, "DEC") == 0) {
        printf("r[%d]: ", reg);
        printf("%d\n", r[reg]);
    } else if (strcmp(display_mode, "HEX") == 0) {
        printf("r[0x%x]: ", reg);
        printf("0x%x\n", r[reg]);
    } else {
        printf("INVALID MODE\n");
    }
}


int readIntFromString(char* source){
    // reads value of integer from source string in correct display mode
    int intsFound;
    int result;

    if (strcmp(display_mode, "DEC") == 0) {
        intsFound = sscanf(source, "%d", &result);
        if (intsFound != 1) {
            printf("INVALID NUMBER - used 0 instead\n");
            result = 0;
        }
    } else if (strcmp(display_mode, "HEX") == 0) {
        intsFound = sscanf(source, "%x", &result);
        if (intsFound != 1) {
            printf("INVALID NUMBER - used 0x0 instead\n");
            result = 0;
        }
    } else {
        printf("INVALID MODE - used 0 instead\n");
        result = 0;
    }

    return(result);
}


void stringUpper(char string[]){
    // upper case the argument string
    int i = 0;

    while ((string[i] != '\0') && (i < SMAX)) {
        if (string[i] >= 'a' && string[i] <= 'z') {
            string[i] = string[i] - 32;
        }
        i++;
    }
}


void clearAllRegisters(){
    int i;
    for (i=0; i<RMAX; i++) {
        r[i] = 0;
    }
}

void clearAllMemory(){
    int i;
    for (i=0; i<MMAX; i++) {
        m[i] = 0;
    }
}


// ============= MAIN PROGRAM ==============

int main () {
    // initialize registers to 0
    clearAllRegisters();

    //initialize memories to 0
    clearAllMemory();

    printf("\nWelcome to the command shell...now with memory!\n");

    while (!done) {
        // GET INPUT
        // show current status and value of r[0]

        printRegister(0);

        if(fromfile == true){
            if(feof(runfp) == 0){
                printf("RUN> %s", cmd_input);
                fgets(cmd_input, SMAX, runfp);
            } else{
                fromfile = false;
                fclose(runfp);
                printf("=====================");
                printf("RUN - end reading from file");
                printf("=====================");
            }
        }
        else{
            //prompt for input and read input string from shell
            printf("> ");
            fgets(cmd_input, SMAX, stdin);
        }

        // break the input string into cmd arg and junk
        wordsFound = sscanf(cmd_input, "%s %s %*s", cmd, arg);

        // uppercase cmd to standard format
        stringUpper(cmd);

        // handle error inputs
        if (wordsFound <= 0) {
            // no command found, substitute NOP
            strcpy(cmd, "NOP");
        } else if (wordsFound <= 1) {
            // no argument found, substitute empty string
            strcpy(arg, "");
        }

        // PROCESS INPUT
        if(strcmp(cmd, "RUN") == 0) {
            printf("=====================\n");
            printf("RUN - start to read from file: %s\n", arg);
            printf("=====================\n");

            runfp = fopen(arg, "r");
            fromfile = true;

        } else if ((strcmp(cmd, "EXIT") == 0) || (strcmp(cmd, "QUIT") == 0)) {
            // exit from shell
            printf("EXIT encountered.\n");
            done = true;

        } else if (strcmp(cmd, "NOP") == 0) {
            // do nothing
            printf("NOP\n");

        } else if (strcmp(cmd, "ECHO") == 0) {
            // echo arg
            printf("%s\n", arg);

        } else if (strcmp(cmd, "MODE") == 0) {
            // update display mode
            // standardize argument
            stringUpper(arg);

            if (strcmp(arg, "DEC") == 0) {
                strcpy(display_mode, "DEC");
            } else if (strcmp(arg, "HEX") == 0) {
                strcpy(display_mode, "HEX");
            } else {
                printf("INVALID DISPLAY MODE: %s\n", arg);
            }

        }  else {
            // Error on Input
            printf(">> Unknown Command |%s|%s|\n", cmd, arg);
        }

    }

    printf("\nEnd Program.\n\n");
    return(0);

}