decoder.c

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

/*
 * The isnumber() function examines the character given as its first
 * argument and returns true if and only if the character represents
 * an number.  This helper function should be relatively short.
 *
 * Returns true if the given character represents an number, false
 * otherwise.
 */
bool isnumber(char c);
/*
 * The decode() function takes a run-length encoded string as its
 * argument, parses every integer n preceding every character in
 * the string, and prints each character n times.  For example, if
 * the string passed to decode() is "1a3b", decode() will print
 * "abbb".  It returns an integer that represents the summed value
 * of the amount of characters printed; in this example, decode()
 * would return the integer 4.
 *
 * This function must also handle malformed run-length encoded strings.
 * A malformed string is any string which does not adhere to the RLE
 * implementation described in the handout. If a malformed string is
 * encountered, it should cease printing the decoded string, print an
 * error message, and return -1.
 *
 * Returns the integer value of the total amount of characters printed,
 * or -1 if the run-length encoded string is malformed.
 */
int decode(char *str);

/*
 * The main function is where C programs begin.
 *
 * This function parses its arguments and returns the value they
 * represent.  In this assignment, the only valid argument is a
 * run-length encoded string.  Any extra arguments in excess of
 * this single valid argument make the invocation of your program
 * invalid.
 *
 * Remember that the argument in argv[0] is the name of the program, so
 * a program passed exactly one argument on the command line will
 * receive _two_ arguments: its name in argv[0] and the provided
 * argument in argv[1].
 *
 * Arguments:
 * argc - The number of arguments received
 * argv - The arguments received as an array of C strings
 *
 * Returns 0 if the argument is well-formed and the string could
 * be decoded, non-zero otherwise.
 */



bool isnumber(char c){
    if (c >= 48 && c <= 57){
        return true;
    }
    else{
        return false;
    }
}

int decode(char *str){
    int n, total, letter;
    total = 0;
    letter = 0;
    n = 0;
    for (int i = 0; str[i] != '\0'; i++){
        if (isnumber(str[i]) == true){
            letter = 0;
            if (n == 0){
                if (str[i] == 0){
                    printf("Not a valid RLE string \n");
                    return -1;
                }
            }
            //line 81 is from K&R page 43 chapter 2.7 (type conversions)
            n = 10 * n + (str[i] - '0');
        }else{
            if (n == 0){
                printf("Not a valid RLE string \n");
                return -1;
            }
            letter += 1;
            if (letter == 2){
                printf("Not a valid RLE string \n");
                return -1;
            }
            for(int e = 0; e < n; e++){
                printf("%c", str[i]);
                if (e == n - 1){
                    total += n;
                    n = 0;
                }
            }
        }
    }
    if (n > 0){
        printf("Not a valid RLE string \n");
        return -1;
    }
    printf("\n");
    return total;
}

int main(int argc, char *argv[]) {
    /* Your main program logic should go here, with helper logic in the
     * functions isnumber() and decode(), which you can place below
     * the closing brace of main() */

/* You should implement isnumber() and decode() here */

    int Valid = 0;
    Valid = decode(argv[1]);
    if (argc == 2) {
        if (Valid == -1){
            printf("Not a valid RLE string \n");
            return -1;
        }else{
            return 0;
        }
    }else{
        return -1;
    }
}