OS PROJECT DIYA

//Group members: Praneetha Sripada and Diya Chandra
//How to compile the program:
//First we need to compile the code gcc osproject1.c --std=c99
//Next to run the file: ./a.out <number of file> <inputfiles name> <outputfile name>
//Input files are input1.txt. input2.txt and input3.txt
#include<stdio.h>//import standard i/p-o/p stream
#include<stdlib.h>//import standard library
#include<sys/signal.h>//import standard signalling
#include<ctype.h>//import character library

int fork(void);//fork function to create process
int getpid(void);//stores pid of child
int getppid(void);//stores pid of parent
int wait(int *);//wait signal for parent to wait till end of process
int createProcess(char[], char[]);//to create child process
int freq(char[], char[]);//to find frequency of each alphabet occuring in the input file
int tolower(int);
int main(int argc, char *argv[]) {
    //argc is length of commandline statement,
    //char* is the length of buffer message & argv[] is the argument array
    if (argc <= 1) {//if n is not given
        printf("Arguments are not given.\n");//buffer error message
        exit(2);//exit if loop
    }
    int no_of_files = atoi(argv[1]);//value of n stored in no_of_files
    if (no_of_files + 3 != argc) {//condition to check if n value is correct
        printf("Input files count are not given properly.\n");//buffer error message
        exit(3);//exit if loop
    }
    int i = 0;
    for (; i < no_of_files; i++) {//call fork process to create child process
        createProcess(argv[i + 2], argv[no_of_files + 2]);//file list in commandline listed after n
    }
    printf("Exiting the Parent Process and all Child Processes are done.\n");//buffer message before
    //terminating
    return 0;
}

//Spawn New Child Processes
int createProcess(char input[], char out[]) {
    int status = 1;
    if (fork() == 0) {//invoke fork function for creation of child
        printf("Child process: %d, parent process :%d\n", getpid(), getppid());//print child and parent pids'
        //frequency count function for the file
        freq(input, out);//call frequency function to find frequency
        exit(0);//exit process
    }
    //wait till the end of the processes
    wait(&status);
    return 0;
}

int freq(char rf[], char wf[]) {
    FILE *writefile;//declare readfile and writefile variables of 'file' type
    char ch;//variable to store each of the characters:a-z
    int count[26];//array to store each of characters:a-z
    int j = 0;
    for (; j < 26; j++) {
        count[j] = 0;
    }//creation of array having 26 contiguous memory spaces for each of
    //the 26 alphabets
    FILE *readfile = fopen(rf, "r");//file is read
    if (readfile == NULL) {//file not found
        fprintf(stderr, "File doesn't exist. Check the file!!\n");//standard error message when file not found
        return 0;
    }
    while ((ch = fgetc(readfile)) != EOF) {//condition to check we are not at the end of file
        if (ch == ' ' && ch == '\n') continue;//ignore spaces and new line statements in file
        count[tolower(ch) - 'a'] = count[tolower(ch) - 'a'] + 1;//move to next consecutive character
    }
    printf("Opening file: %s and reading data\n", rf);/*buffer message to guide user on the filename being read
    read characters and store the count in array.*/

    fclose(readfile);//close file after reading
    writefile = fopen(wf, "a");//file is written
    fprintf(writefile, "%s\n", rf);
    //write the frequency to the output file
    int i = 0;
    for (; i < 26; i++) {
        fprintf(writefile, "%c -> %d\n", i + 'a', count[i]);
    }
    fclose(writefile);//close file after writing
    printf("Writing frequency of Characters to output file is completed.\n");//buffer message to indicate
    //process completion
    //free(count);//free up the memory
    return 0;
}