Undefined reference error to function that is actually defined in C - c

Question

I wrote this program to build a number diamond. The issue is that when I compile the program, it throws the error
build2.c:(.text+0x5): undefined reference to `get_input'
collect2: error: ld returned 1 exit status
I've tried for hours to figure out what exactly the problem is (e.g. if there is a spelling mistake or something similar), but the function call looks identical. I have attempted to rename it, write it as both a prototype and as an implementation, and nothing seems to work. Is there an issue that I'm not seeing?
//Define prior to main
int is_valid(int);
int get_input(void);
void print_pattern(int);
//Main
int main(void){
int diamond_size;
//diamond_size = get_input();
//value from get imput method used for diamond size
print_pattern(get_input());
return 0;
}
void print_pattern(int size){
int length, num, i, j;
//beginning of new diamond
printf("\n");
//Define each integer to work in layout of diamond
//First for loop fans out
for(i=1; i <= size; i += 2){
length = size-i+1;
num = 1;
printf("%*s", length," ");
for(j = 0; j < i; j++){
printf("%d ", num);
num++;
}
printf("\n");
}
//second for loop fans in
for(i=size-2; i >= 1; i -= 2){
length = size-i+1;
num = 1;
printf("%*s", length," ");
for(j = 0; j < i; j++){
printf("%d ", num);
num++;
}
printf("\n");
}
int is_valid(int value){
int rem;
//uses remainder to determine if it is odd or even; an even number will not have a reaminder in this case
rem = value % 2;
if (rem == 0){
printf("You've entered a even number. Please try again.\n");
return (0);
}
//greater than 9 cnd
if (value > 9){
printf("You have entered a number greater than 9. Please try again.\n");
return (0);
}
//less than 1 cnd
if (value < 1){
printf("You have entered a number less than 1. Please try again.\n");
return (0);
}
return (1);
}
int get_input()
{
int cont, number, valid;
cont = 1;
while (cont = 1)
{
printf("Enter an odd number less than 9 and greater than 0 < ");
scanf("%d", &number);
valid = is_valid(number);
if (valid == 1)
{
cont = 0;
}
}
return number;
}
}

Answer 1

You seem to have nested functions; this is (a) a non-standard GCC extension, and (b) I presume the scope of the nested get_input() function is the enclosing function, not the file scope. The solution is to move get_input() to file scope. At the end of print_pattern() add an extra }, and delete the final } at the end of the file.
Also, please format your code - most IDEs these days have options to tidy it up, and with correct indentation you may have seen your problem earlier.
Oh, and as a bonus bug fix, you also have in get_input():
while (cont = 1)
This will always be true - use this instead:
while (cont == 1)

Answer 2

The function print_pattern is not terminated at proper place but instead at the very end of the file:
void print_pattern(int size){
...
... end of the loop
}
... more functions
...
... end of print_pattern
}
This results into defining nested functions instead of global level.
It's generally good habit to indent the blocks, in which case you would realized the mistake very quickly.