Help with scanf and memory allocation - c

Question

Here is my code:
#include <stdio.h>
#include <stdlib.h>
#define MAX 50
float** getdata(void);
void calculations(float* fPtr);
//void printoriginal(float* values, int inputnum, float* fPtr);
int main(void)
{
float** fPtr;
float* values;
fPtr = getdata();
calculations(*fPtr);
int element;
// printoriginal(*values, inputnum, *fPtr);
system("PAUSE");
return 0;
}
float getvalues(void)
{
float* values = (float*)calloc(*inputnum, sizeof(float));
float** getdata(void)
{
int i;
int n;
float** fPtr;
int* inputnum;
printf("How many values do you want to input into the array?");
scanf("%d", inputnum);
float* values = (float*)calloc(*inputnum, sizeof(float));
if (values == NULL)
{ printf("Memory overflow\n");
exit(101);
}
for(i = 0; i < *inputnum; i++)
{
n = i + 1;
printf("Please enter your %d number: ", n);
scanf("%f",(values+i));
}
fPtr = (float**)calloc(*inputnum+1, sizeof(float*));
if (fPtr == NULL)
{ printf("Memory overflow\n");
exit(101);
}
for(int c=0; c < *inputnum; c++)
{
*(fPtr+i) = (values+i);
}
printf("%f", values+2);
return fPtr;
}
I scanf the values in getdata, but I am scanning in garbage. Im pretty certain my scanf is off. Also, how would I be able to pass back my values array through reference?? I am having a very hard time with that as well. Thanks everyone.

Answer 1

Instead of
int * inputnum;
scanf( ..., inputnum );
you want:
int inputnum;
scanf( ..., &inputnum );
Either that, or you need to insert an allocation of inputnum:
/* Very non-C-worthy code sample */
int * inputnum;
inputnum = malloc( sizeof *inputnum );
if( inputnum == NULL ) {
perror( "malloc" );
exit( EXIT_FAILURE );
}
scanf( ..., inputnum );
but that will look very strange to anyone familiar with C
(Unless there is some other reason for it, and in this
case there does not appear to be any reason.)
The problem you are experiencing is that the scanf is
storing the received value in the location pointed to
by inputnum, which is a bogus location since inputnum
is uninitialized.

Answer 2

I like to have objects "assigned" to one single function. In your program, your values are created in the function getdata(), used in calculations() and never released.
If the main() function was responsible for them, it would make coding easier, in my opinion. Something like
int main(void) {
int inputnum, innum;
double *fPtr;
printf("How many values do you want to input into the array?");
fflush(stdout);
if (scanf("%d", &inputnum) != 1) {
fprintf(stderr, "Error in input. Program aborted.\n");
exit(EXIT_FAILURE);
}
if (inputnum > MAX) { /* ... nothing yet ... */ }
fPtr = calloc(inputnum, sizeof *fPtr);
if (fPtr == NULL) {
fprintf(stderr, "Not enough memory. Program aborted.\n");
exit(EXIT_FAILURE);
}
/* use fPtr in other functions */
innum = data_get(fPtr, inputnum);
data_print(fPtr, innum);
free(fPtr);
return 0;
}
In the snippet above, I used the functions data_get() and data_print() with a somewhat different prototype than you have. These functions take a pointer and a number of elements.
int data_get(double *data, int num);
void data_print(double *data, int num);
The first one reads up to num doubles into the memory pointed to by data and returns the number of doubles that was effectively entered.
The second takes number of doubles to print.
Oh! Unless you have a very good reason to use floats, don't use them. Always prefer doubles.

Answer 3

Also Instead of
printf("%f", values+2);
use
printf("%f", *(values+2));

Answer 4

There is so many errors, I didn't know where to start :)
Code completely rewritten below. Please study this.
#include <stdio.h>
#include <stdlib.h>
#define MAX 50
int get_data (float** array); /* must be pointer-to-pointer to return through parameter */
void print_data (const float* array, int size); /* print data */
void do_weird_things (float* array, int size); /* do weird things with the data */
void clear_data (float* array); /* clean up */
int main(void)
{
float* array;
int size;
size = get_data (&array);
printf("Before weird things:\n");
print_data (array, size);
do_weird_things (array, size);
printf("After weird things:\n");
print_data (array, size);
clear_data (array);
system("PAUSE");
return 0;
}
int get_data (float** array)
{
int i;
int items;
printf("How many values do you want to input into the array? ");
scanf("%d", &items);
getchar(); /* remove \n from stdin */
*array = calloc(items, sizeof(float));
if (*array == NULL)
{
printf("Memory overflow\n");
exit(EXIT_FAILURE);
}
for(i = 0; i < items; i++)
{
printf("Please enter your %d number: ", i+1);
scanf("%f", (*array) + i);
getchar(); /* remove \n from stdin */
}
return items;
}
void do_weird_things (float* array, int size) /* do whatever data manipulation you wish here */
{
int i;
for(i=0; i<size; i++)
{
array[i] += i;
}
}
void print_data (const float* array, int size)
{
int i;
for(i=0; i<size; i++)
{
printf("%f\t", array[i]);
}
printf("\n");
}
void clear_data (float* array)
{
free(array);
}