Continued Power Function Message - c

Question

I keep getting the error message that my I have an undefined reference to the power function, but I'm not really sure where that is occurring or why my code is coming up with that error because I have used to power function before in this way. If anyone could help me figure out why it isn't working now I would really appreciate it.
#include "stdio.h"
#include "string.h" //Needed for strlen()
#include "math.h"
#define MAX_BITS 32
#define MAX_LENGTH 49
#define NUMBER_TWO 2
#define NUMBER_ONE 1
#define TERMINATOR '\0'
//Code to find the index of where the string ends
int last_index_of(char in_str[], char ch) {
for (int i = 0; i < MAX_LENGTH; i++) {
if(in_str[i] == ch) {
last_index_of == i;
}
}
return last_index_of;
}
//Code to find the start of the fractional aspect
void sub_string(char in_str[], char out_str[], int start, int end){
int i = 0;
while (i < 1) {
out_str[i] = in_str[start] + in_str[end-1];
i++;
}
}
int main()
{
//Declaration of variable
char input[MAX_LENGTH +1]; // +1 for '\0'
int number;
double exponent;
char output[MAX_BITS];
int fraction;
sub_string(input, output, 0, TERMINATOR);
//Input from the user
printf("Enter a floating point value in binary: ");
scanf("%s", input);
//Calculates the Decimal Part
for (int i = 0; i < last_index_of(input, TERMINATOR) ; i++) {
number = number + number + input[i];
}
printf("%d", number);
exponent = -1;
//Calculates the Fractional Part
for (int j = 0; j < last_index_of(input, TERMINATOR); j++) {
if (j == last_index_of) {
fraction = NUMBER_ONE/(pow(NUMBER_TWO, exponent));
printf("%d/n", fraction);
}
else {
fraction = NUMBER_ONE/(pow(NUMBER_TWO, exponent));
printf("%d + ", fraction);
exponent--;
}
}
return 0;
}

Answer 1

Some problems:
you need -lm option to linker to tell it where to find pow function
last_index_of is not correctly written, you use the function name as an internal variable, you can correct it this way:
//Code to find the index of where the string ends
int last_index_of(char in_str[], char ch) {
int ret = 0;
for (int i = 0; i < MAX_LENGTH; i++) {
if(in_str[i] == ch) {
ret = i;
}
}
return ret;
}
Note that you can replace your last_index_of() function by strlen()
as pointed in comment, sub_string() is not functionnal. A corrected version could be:
//Code to find the start of the fractional aspect
void sub_string(char in_str[], char out_str[], int start, int end){
int i = 0;
while (start != end) {
/* warning, bounds are still not tested...*/
out_str[i++] = in_str[start++];
}
out_str[i] = '\0'
}
Instead of calling last_index_of() in your exist for loop condition, you should take its value to re-use it:
for (int j = 0; j < last_index_of(input, TERMINATOR); j++) {
/* Error here: will never be TRUE */
if (j == last_index_of) {
/* ... */
}
else {
/* ... */
}
}
would become:
int last_index = last_index_of(input, TERMINATOR);
for (int j = 0; j < last_index; j++) {
if (j == last_index) {
/* ... */
}
else {
/* ... */
}
}
Another problem, you use number variable without initializing it, you should write int number = 0 instead of int number;
After that, there is also a problem with your logic.
You have some idea of what you want to do, but it is not clear in your code.
It seems that you want
the user to input some string in the form 10010.100111
to split this string into two parts 10010 and 100111
to convert the first part into integer part 10010 -> 18
to convert the second part into fractional part 100111 -> 0.609...
This decomposition may lead you to write this kind of code:
#include "stdio.h"
#include "string.h"
#define MAX_BITS 32
#define MAX_LENGTH 49
//Code to find the index of where the string ends
int last_index_of(char in_str[], char ch)
{
int ret = 0;
for (int i = 0; i < MAX_LENGTH; i++) {
if (in_str[i] == ch) {
ret = i;
}
}
return ret;
}
void sub_string(char in_str[], char out_str[], int start, int end)
{
int i = 0;
while (start != end) {
/* warning, bounds are still not tested... */
out_str[i++] = in_str[start++];
}
out_str[i] = '\0';
}
void split(char *input, char *first, char *second)
{
int idx = last_index_of(input, '.');
sub_string(input, first, 0, idx);
sub_string(input, second, idx + 1, strlen(input));
}
int main()
{
//Declaration of variable
char input[MAX_LENGTH + 1]; // +1 for '\0'
char first[MAX_BITS];
char second[MAX_BITS];
/* Input from the user */
printf("Enter a floating point value in binary: ");
scanf("%s", input);
/* split integer and fractionnal parts */
split(input, first, second);
/* decode integer part */
printf("integer part:\n");
for (int i = strlen(first) - 1, j = 1; i > -1; --i, j <<= 1) {
if (first[i] == '1') {
printf("%d ", j);
}
}
/* decode frac part */
printf("\nfractionnal part:\n");
for (int i = 0; i < strlen(second); ++i) {
if (second[i] == '1') {
printf("1/%d ", 2 << i);
}
}
return 0;
}