Thread: program adding numbers using desired base doesn't show any output

Hello, I have a problem with an "add calculator".
Valgrind reports no memory errors, no errors from compiler but the program doesn't show any output despite the printf - "Result is zero".

All pointers, and variables are (n my opinion) correctly initialized.
getnum function gets a number, returns a pointer to char *,
add function processes two numbers as strings, returns result which is a pointer to char (char *) as well.

Trying to work it out for the past 4 hours and can't find a mistake.
Thanks in advance!

Here's the code (sorry, it's quite long):

Code:

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

#define MAX(A,B) ((A)>(B) ? (A) : (B))

char *getnum(FILE *infile, int base)
{
    int len = 10;
    int c;
    int pos = 0;
    char *num = NULL; 
    char *tmpnum = NULL;
    
    num = malloc(sizeof(char)*len);
    if(num == NULL) {
        perror("malloc fail");
        return NULL;
    }
    while (((c = fgetc(infile)) != EOF) && (isalnum(c))) {
        num[pos++] = c;
        if (isdigit(c)) {
            if (c >= base + '0') {
                fprintf(stderr, "Wrong base\n");
                free(num);
                return NULL;
            }
        }
        else if (isalpha(c)) {
            if ( c >= base + '0' + 7) {
                fprintf(stderr, "Wrong base, expected 16\n");
                free(num);
                return NULL; 
            }
        }
        if (pos >= len) {
            len *= 2;
            tmpnum = realloc(num, len*sizeof(char));
            if (tmpnum == NULL) {
                perror("realloc fail");
                free(num);
                return NULL;
            }
            else num = tmpnum;
        }
    }
    num[pos] = '\0';
    return num;            
}

char *add(char *no1, char *no2, int base)
{
    int len1, len2, length, i, j, pos, adder = 0;
    char *result = NULL; 
    char *tmp1 = NULL;
    char *tmp2 = NULL;
    
    len1 = strlen(no1);
    len2 = strlen(no2);
    length = MAX(len1, len2);
    if (len1 == 1 && len2 == 1) {
        length++;
    }    
    result = malloc((length + 1)*sizeof(char));
    if (result == NULL) {
        perror("malloc fail");
        free(result);
        return NULL;
    }
    tmp1 = realloc(no1, (length + 1)*sizeof(char));             
    if (tmp1 == NULL) {
        perror("realloc fail");
        free(result);
        return NULL;
    } else {
        no1 = tmp1;
    }
    tmp2 = realloc(no2, (length + 1)*sizeof(char));                
    if (tmp2 == NULL) {
        perror("realloc fail");
        free(result);
        free(no1);
        return NULL;
    } else {
        no2 = tmp2;
    }
    for (i = length - 1, j = len1 - 1; j >= 0; i--, j--) {
        no1[i] = no1[j];
    }
    for (i = 0; i < (length - len1); i++) {
        no1[i] = '0';
    }
    no1[length] = '\0';

    for (i = length - 1, j = len2 - 1; j >= 0; i--, j--) {
        no2[i] = no2[j];
    }
    for (i = 0; i < (length - len2); i++) {
        no2[i] = '0';
    }
    no2[length] = '\0';
    
    pos = length - 1;
    
    while (pos >= 0) {
        if (no1[pos] > '9') {
            no1[pos] -=7;
        }            
        if (no2[pos] > '9') {
            no2[pos] -=7;
        }
        result[pos] = no1[pos] + no2[pos] + adder - '0';
        adder = 0;
        if (result[pos] >= (base + '0')) {
            result[pos] -= base;
            adder = 1;
        }
        if (result[pos] > '9') {
            result[pos] += 7;
        }
        pos--;
    }
    result[length] = '\0';
    free(no1);
    free(no2);
    return result;
}    
    
int main(int argc, char **argv)
{
    FILE *infile = NULL;
    char *number1 = NULL;
    char *number2 = NULL;
    char *result = NULL;
    int base, i, j = 0, length, count = 0;
    
    if (argc != 3) {
        printf("usage: ./add infile.txt base\n");
        return -1;
    }
    infile = fopen(argv[1], "r");
    if (infile == NULL) {
        perror("infile open failed");
        return -1;
    }
    base  = atoi(argv[2]);
    while (!feof(infile)) {
        number1 = getnum(infile, base);
        if (number1 == NULL) {
            fclose(infile);
            return -1;
        }
        number2 = getnum(infile, base);
        if (number2 == NULL) {
            fclose(infile);
            free(number1);
            break;                             /* or return ? */
        }                
        break;
    }
    printf("Base is %d\n", base);
    result = add(number1, number2, base);
    if (result == NULL) {
        free(number1);
        free(number2);
        fclose(infile);
        return -1;
    }
    length = strlen(result);
    for (i = 0; i <= length - 1; i++) {
        if (result[i] == '0') {
            count++;
        }
    }
    if (count == length) {
        printf("Result is 0\n");
        free(result);
        result = NULL;                     /* arguable */
        fclose(infile);
        return 0;
    }
    for (i = 0; i <= length - 1; i++) {
        if (result[i] != '0') {
            break;
        }
    }
    for (j = i; j == (length - 1); j++) {
        printf("Result is: %s\n", &result[j]);
        break;
    }
    free(result);
    result = NULL;
    fclose(infile);
    return 0;
}

OMG oogabooga You helped me a lot!
I'd never get to that, I was expecting memory management is incorrect, and I was looking into it mainly.
The program is supposed to run as

Code:

./name input.txt base

, where instead of base you put desired base eg. 2 or 10.

Actually, I should also mention that your main loop is very very wrong. It won't loop through all the numbers in the file, but only get the last two for processing.

Hmm after giving it much thought I'd suspect it of processing only two numbers from the beginning, not from the end?

Thanks for reply. I have another question though. How to implement contnuous search and assignment for new numbers read from file. I mean, firstly assign

Code:

number = getnum(infile, base)

and then how to pass that varying number of arguments to add function? Because it only operates on two numbers at a time.
If anybody knows, please provide me with information, I don't demand code or even pseudocode; even suggestion is VERY MUCH appreciated.

If I understand your question correctly, you could write the function to receive a variable number of arguments. Or you could store the values you want in an array, with the next element of that array a key that indicates it's the end of arguments, and pass that array to your function.

Originally Posted by Matticus

If I understand your question correctly, you could write the function to receive a variable number of arguments. Or you could store the values you want in an array, with the next element of that array a key that indicates it's the end of arguments, and pass that array to your function.

If I decide to store it in an array that would be a two-dimensional array. Then how to pass those strings, two at a time, and keep the result of the previous operation as one of the parameters passed to add function?

Originally Posted by oogabooga

I'm also taking a guess at what you actually mean, so this might not be what you want but...

You could pass the first two numbers to the add function and get the result. Then read the next number and pass that and the result to add. Then read the next number, etc. When you're out of numbers, print the result.

I did as You advised. However, now program hangs after invoking, and I have to press Ctrl+C to stop it.
I only changed main(), posting it below:

Code:

int main(int argc, char **argv)
{
    FILE *infile = NULL;
    char *number1 = NULL;
    char *number2 = NULL;
    char *number_next = NULL;
    char *result = NULL;
    
    int base, length, count = 0;
    
    if (argc != 3) {
        printf("usage: ./add infile.txt base\n");
        return -1;
    }
    infile = fopen(argv[1], "r");
    if (infile == NULL) {
        perror("infile open failed");
        return -1;
    }
    base  = atoi(argv[2]);
    while (feof(infile) == 0) {
        number1 = getnum(infile, base);
        if (number1 == NULL) {
            fclose(infile);
            return -1;
        }
        number2 = getnum(infile, base);
        if (number2 == NULL) {
            fclose(infile);                    
            free(number1);                        
            return -1;                             /* or  BREAK ? */
        }                
        break;
    }
    
    result = add(number1, number2, base);
    if (result == NULL) {
        free(number1);
        free(number2);
        fclose(infile);
        return -1;
    }
    /*result_update = add(result, number3, base);*/
    while (((number_next = getnum(infile, base)) != NULL) || (feof(infile) == 0)) {
        result = add(result, number_next, base);
    }    
        
    
    length = strlen(result);
    
    for (count = 0; count < length; count++) {
        if (result[count] != '0')
            break;
    }
    if (count == length) {
        printf("Result is 0\n");
        free(result);
        result = NULL;                     /* arguable */
        fclose(infile);
        return 0;
    }
    printf("Result is: %s\n", &result[count]);
    printf("Base is %d\n", base);
    free(result);
    result = NULL;
    fclose(infile);
    return 0;
}

Originally Posted by oogabooga

You're right! I didn't see the break at the end there. (And even without it, it will actually not process any numbers at all!) Still, it's probably not what you want. Presumably you want that loop to control most of the code that comes after it so that each group of two numbers is added.

Once you've extended the body of the loop, a better loop condition is:

Code:

while ((number1 = getnum(infile, base)) != NULL) {
//....

@Matticus - I got it working, thank You!


@oogabooga I quoted your post, why did you suggest that change in while condition? Is the one presented in the code in the first post prone to some overflow or bugs?

will return a new chunk of memory to result, but is not freeing the old memory pointed to by result.

valgrind -v gives me no errors, so I guess no memory leak there.

Also in post#9, the first while loop in main is not a loop at all, since it ends in a break (i.e., it can only execute it's block of code once). At best it's an if statement, except that it's condition will always be true when it is first hit, so it's kind of pointless.

Fixed, thank You.
But, condition

Code:

(feof(infile) == 0) 

is not always true. What if a file would be empty?

Does your program work with input like this (base 10) ?
1111
9999

How about this (base 16) ?
aaaa
cccc

Yeah, I got it already, change length assignment

Originally Posted by Pole

But, condition

Code:

(feof(infile) == 0) 

is not always true. What if a file would be empty?

It would still not be true before you failed to read from the file.

That is why it is better to use the return from a read function to control loops.

Kurt

Originally Posted by ZuK

It would still not be true before you failed to read from the file.

That is why it is better to use the return from a read function to control loops.

Kurt

So I guess I should add

Code:

((feof(infile) == 0) || (number1 = getnum(infile, base) != NULL )) 

number1 instead of number 2, as @oogabooga said.