how to stop my program from skipping characters before saving them - c

Question

I am making a simple program to read from a file character by character, puts them into tmp and then puts tmp in input[i]. However, the program saves a character in tmp and then saves the next character in input[i]. How do I make it not skip that first character?
I've tried to read into input[i] right away but then I wasn't able to check for EOF flag.
FILE * file = fopen("input.txt", "r");
char tmp;
char input[5];
tmp= getc(file);
input[0]= tmp;
int i=0;
while((tmp != ' ') && (tmp != '\n') && (tmp != EOF)){
tmp= getc(file);
input[i]=tmp;
length++;
i++;
}
printf("%s",input);
It's supposed to print "ADD $02", but instead it prints "DD 02".

Answer 1

You are doing things in the wrong order in your code: The way your code is structures, reading and storing the first char is moved out of the loop. In the loop, that char is then overwritten. In that case start with i = 1.
Perhaps you want to read the first character anyway, but I guess you want to read everything up to the first space, which might be the first character. Then do this:
#include <stdio.h>
int main(void)
{
char input[80];
int i = 0;
int c = getchar();
while (c != ' ' && c != '\n' && c != EOF) {
if (i + 1 < sizeof(input)) { // store char if the is room
input[i++] = c;
}
c = getchar();
}
input[i] = '\0'; // null-terminate input
puts(input);
return 0;
}
Things to note:
The first character is read before the loop. the loop condition and the code that stores the char then use that char. Just before the end of the loop body, the next char is read, which will then be processed in the next iteration.
You don't enforce that the char buffer input cannot be overwritten. This is dangerous, especially since your buffer is tiny.
When you construct strings char by char, you should null-terminate it by placing an explicit '\0' at the end. You have to make sure that there is space for that terminator. Nearly all system functions like puts or printf("%s", ...) expect the string to be null-terminated.
Make the result of getchar an int, so that you can distinguish between all valid character codes and the special value EOF.
The code above is useful if the first and subsequent calls to get the next item are different, for example when tokenizing a string with strtok. Here, you can also choose another approach:
while (1) { // "infinite loop"
int c = getchar(); // read a char first thing in a loop
if (c == ' ' || c == '\n' || c == EOF) break;
// explicit break when done
if (i + 1 < sizeof(input)) {
input[i++] = c;
}
}
This approach has the logic of processing the chars in the loop body only, but you must wrap it in an infinite loop and then use the explicit break.