Thread: help with error

So now I've got the warnings down to fscanf and fopen are unsafe and one other:

warning C4047: '=' : 'char' differs in levels of indirection from 'void *'
line 61, which is

Code:

 *(a+p) = ch;

I'm not quite sure what that means...

Originally Posted by arrgh

So now I've got the warnings down to fscanf and fopen are unsafe and one other:

warning C4047: '=' : 'char' differs in levels of indirection from 'void *'
line 61, which is

Code:

 *(a+p) = ch;

I'm not quite sure what that means...

My guess: you defined a as a void ** (or somehow defined ch as a void *, I suppose).

I think I've found the problem. I'm supposed to read in 10 polynomials from a file, but there's only 9 available, so the last should be a 0. I remember someone saying that calloc creates a block of memory and clears it, so shouldn't the elements in the array just be 0? If not, how would I check to see if there is 0 polynomial or if the array is empty?

Code:

int main(void) {

	FILE *text;
	int number, exp, p, k, i, go, poly1, poly2;
	float coeff;
	char again = 'Y', newFile = 'Y', operation, ch;
	char fileName[NAME], *polynomial[MAXPOLY], charArray[MAXPOLY], *token, *a;
	struct poly *first = NULL, *sum, *multiply1, *multiply2, *newLink, *pointers;

	while(newFile == 'Y' || newFile == 'y') {
		printf("\nEnter the file where the polynomials are found: \n");
		fscanf(stdin, " %s", fileName);  //fgets(fileName, NAME, stdin);  
		text = fopen(fileName, "r");
/* If file failed to open, print error statement and ask for a different file. */
		if(text == NULL) {
			printf("Error involved in opening file. Cannot open %s\n", fileName);
			continue;
		}
		fscanf(text, " %d", &number);
/* Create an array of pointers. If error involved in allocating memory, terminate program. */
		pointers = calloc(number, sizeof(struct poly));
		if(pointers == NULL) {
			printf("Error involved in allocating space. Cannot complete task.");
			break;
		}

		a = &charArray[0];
		ch = fgetc(text);
		for(k = 0; k < number; k++) {
			for(p = 0; ; p++) {
				ch = fgetc(text);
				*(a+p) = ch;
				if(ch == '\n') {
					*(a+p+1) = NULL;
					break;
				}
			}
			polynomial[k] = a;
			if(k < number - 1) {
				a = calloc(1,MAXPOLY*sizeof(char));
				if(a == NULL) {
					printf("Error involved in allocating space. Cannot complete task.");
					exit(EXIT_FAILURE);
				}
			}
		}
		printf("\nThe polynomials available for operation are: \n");
		for(i = 0; i < number; i++) {
			a = polynomial[i];
			printf("%d. %s", i+1, a+i);
		}
		printf("\nWhat operation would you like to perform? \n1. ADD polynomials \n2. MULTIPLY polynomials \n3. EVALUATE polynomial\n");
		for(;;) {
			printf("\nEnter choice # --> \n");
			fscanf(stdin, " %c", &operation);
			if(operation > '3' || operation < '1') {
				printf("Invalid. Please select again.");
				continue;
			}
			break;
		}
		for(;;) {
			printf("Enter the polynomials you would like to work with: (#,# format)\n");
			fscanf(stdin, " %d, %d", &poly1, &poly2);
			if(poly1 < 1 || poly2 < 1 || poly1 > number || poly2 > number) {
				printf("Error. Please select again.");
				continue;
			}
			break;
		}
	return 0;
}

ok, new code. I'm not sure if I'm using the fgets right, since I usually get by with looping scanf("%c"...), but since the program works, I think I'm going in the right direction. I haven't freed anything since I still have to make a linked list, which is a whole other problem. At the moment, I'm trying to print out the polynomials. I've gone through, step-by-step, and the string that's stored is correct, but when the program prints out the polynomials, it cuts off the first couple of characters. So for example, from the following file, the program prints out the entire first polynomial, then leaves off the 8, the 21, and then the x^4.

Code:

10
26x^5 + 5x^2 + 323x^3 + 50x^2 + 14x
8x^3 + 11x^2 + 34x + 4
21x^6 + 3x^5 + 4x + 4
x^4 + x^2 + x
 .
 .
 .

Code:

int main(void) {

	FILE *text;
	int number, exp, p, k, i, go, poly1, poly2;
	float coeff;
	char again = 'Y', newFile = 'Y', operation, ch;
	char fileName[NAME], *polynomial[MAXPOLY], *token, *a;
	struct poly *first = NULL, *sum, *multiply1, *multiply2, *newLink, *pointers;

	while(newFile == 'Y' || newFile == 'y') {
		printf("\nEnter the file where the polynomials are found: \n");
		fscanf(stdin, " %s", fileName);  //fgets(fileName, NAME, stdin);  
		text = fopen(fileName, "r");
/* If file failed to open, print error statement and ask for a different file. */
		if(text == NULL) {
			printf("Error involved in opening file. Cannot open %s\n", fileName);
			continue;
		}
		fscanf(text, " %d", &number);
/* Create an array of pointers. If error involved in allocating memory, terminate program. */
		pointers = calloc(number, sizeof(struct poly));
		if(pointers == NULL) {
			printf("Error involved in allocating space. Cannot complete task.");
			break;
		}

		ch = fgetc(text);
		for(k = 0; k < number; k++) {
			a = calloc(1, MAXPOLY*sizeof(char));
			fgets(a,MAXPOLY*sizeof(char),text);
			*(polynomial + k) = a;
		}
		printf("\nThe polynomials available for operation are: \n");
		for(i = 0; i < number; i++) {
			a = polynomial[i];
			printf("%d. %s", i+1, a+i);
		}
		printf("\nWhat operation would you like to perform? \n1. ADD polynomials \n2. MULTIPLY polynomials \n3. EVALUATE polynomial\n");
		for(;;) {
			printf("\nEnter choice # --> \n");
			fscanf(stdin, " %c", &operation);
			if(operation > '3' || operation < '1') {
				printf("Invalid. Please select again.");
				continue;
			}
			break;
		}
		for(;;) {
			printf("Enter the polynomials you would like to work with: (#,# format)\n");
			fscanf(stdin, " %d, %d", &poly1, &poly2);
			if(poly1 < 1 || poly2 < 1 || poly1 > number || poly2 > number) {
				printf("Error. Please select again.");
				continue;
			}
			break;
		}

		printf("\nThe symbolic sum of the 2 polynomials is: ");



		

	}

	free(pointers);
	return 0;
}

You want to printf a, not a+i (you're cutting off the first i characters of a that way).

Hehe, oops... Thanks!

Since the 10th polynomial doesn't exist, how would you change the empty array to 0? Could you just insert an if statement checking whether each array is "" and then replace with '0'?

Originally Posted by arrgh

Hehe, oops... Thanks!

Since the 10th polynomial doesn't exist, how would you change the empty array to 0? Could you just insert an if statement checking whether each array is "" and then replace with '0'?

Do you expect your users to lie to you? The 10 was in the file.

Anyway, if the array is "", then that's what you want -- you want an empty string. Or do you mean you want it to become the polynomial "0"?

The first number is supposed to be the number of polynomials in the file. So the empty string should be polynomial "0".

Originally Posted by arrgh

The first number is supposed to be the number of polynomials in the file. So the empty string should be polynomial "0".

fgets returns NULL if nothing was read (due to end-of-file or whatever) -- so when you read a line in, check the return value of fgets (a la

Code:

char *bob;
bob = fgets(whatever your parameters were);
if (bob == NULL) {
    /* copy "0" into the appropriate place */
}

YAY, everything works... Thanks, everybody!!

Now, next question: What would the function header for a function that returns an array of pointers to structures and takes in an array of pointers look like?

Originally Posted by arrgh

YAY, everything works... Thanks, everybody!!

Now, next question: What would the function header for a function that returns an array of pointers to structures and takes in an array of pointers look like?

Hah -- that's easy:

Code:

That's because you can't return an array. You could pass the return array in as a parameter:

Code:

function(struct polynomial *in[], struct polynomial *out[])

Remember, you can't assign to an array name.