Strange character appearing at start of string - c

Question

I am taking different transistor data from a file. The program stores that in a structure. It then prompts for an input from the user. User enters 5 different values, eg 12 0.03 100 320 65 and then the program takes these values and compares it to the data from the file and sees if any transistors would be suitable for the parameters you have entered.
The program then prompts the user again, and this repeats until the letter q is entered, which ends the program.
The problem I'm having - and I've been trawling the internet for hours trying to find a solution but none of them have worked - is that any input after the first set isn't accepted. So it looks like this.
Please input: Voltage Current Power Frequency Gain
15 0.1 200 100 80
15 0.1 200 100 80
ALL RELEVANT TRANSISTORS
Please input: Voltage Current Power Frequency Gain
20 0.3 100 150 40
?1 2 3 4 5
The question mark is always a strange character. In the past few hours it has been a ? in a diamond, the letter P, and a small square with 0010 in it. Everything I have found on the internet says this should work. What am I missing?
Here's my input function
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#define MAX 15
struct input{
int volt, power, freq, gain;
float amp;
};
struct input inputs[MAX_IN];
int CHK =1, number=0;
int input_function1()
{
const char check[3] = {'\0'};
int i;
const char inp[30] = {'\0'};
printf("Please input: Voltage Current Power Frequency Gain\n");
fgets(inp, 30, stdin);
puts(inp); //Prints out the string to see if the input has been correctly accepted
ungetc(inp, stdin);
sscanf(inp, "%s", &check);
if(check[0]!='q' && check[1]!='q' && check[2]!='q')
{
sscanf(inp, "%d %f %d %d %d", &inputs[number].volt, &inputs[number].amp,
&inputs[number].power, &inputs[number].freq, &inputs[number].gain);
}
}
Below is how I am calling the function. check_function is the function which checks the input transistor against the database.
while(CHK==1)
{
input_function1();
check_function();
++number;
}

Answer 1

You are declaring a const char array like this:
const char test[30] = {'\0'};
and that actually creates a string/array that is not editable and the terminating 0 that should mark the end of a string is the only character in this array. Also this zero is being set at the test[0].

Answer 2

Here's a little example which fixes some stuff of your current snippet:
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <conio.h>
#define MAX 15
struct input {
int volt, power, freq, gain;
float amp;
};
struct input inputs[MAX];
int fill_input(int index) {
char check[4];
char inp[30];
printf("Please input: Voltage Current Power Frequency Gain\n");
fgets(inp, 30, stdin);
puts(inp);
sscanf(inp, "%s", &check);
if (strcmp(check, "qqq") == 0) {
return 0;
}
sscanf(inp, "%d %f %d %d %d", &inputs[index].volt, &inputs[index].amp,
&inputs[index].power, &inputs[index].freq, &inputs[index].gain);
return 1;
}
int main(int argc, char *argv[]) {
int index = 0;
while (1 && index < MAX) {
if (!fill_input(index)) break;
index++;
}
printf("End");
getch();
}
The goal of the above snippet is to help you to move on.
Few notes for you to consider though:
Try to avoid global variables as much as possible
The current provided version is far away from being optimal, think why is that and don't just copy paste other's code, try to figure out what a good function is all about. The most important lesson for you here should be how to code proper functions
The errors in your snippet are related to arguments not matching properly the datatypes, for instance, take a look to the fgets docs, you can see the first argument is char*, you were using const char*, datatypes should match
Try to refactor the function till is good one and learn as much as possible from each refactoring
Have fun coding! <--- most important one