Issue with variable values in C (huge numbers)

I'm just start to learn C and I came across with an exercise to count the number of new lines(\n), blank spaces and tabs(\t) in stdin.

The question is,

Why:

#include <stdio.h>

int main(void){

    int c, nl, ns, nt = 0;

    while ((c = getchar()) != EOF) {

        if (c == '\n') {

            ++nl;

        }

        else if (c == '\t') {

            ++nt;
           
        }
        else if (c == ' ') {

            ++ns;

        }

    }

    printf("Lines: %d, Tabs: %d, Spaces: %d", nl, nt, ns);

    
    return 0;
}

Gives me different huge and wrongs numbers based on how I provide data to program?

Using ./a.out and typing "a" in terminal, followed by Ctrl + D:

Lines: -621574383, Tabs: 0, Spaces: 32765

Using cat input.txt | ./a.out, with input.txt containing "a" and nothing more:

Lines: -115774576, Tabs: 0, Spaces: 32765

Using ./a.out <<< echo 'a':

Lines: 1775654849, Tabs: 0, Spaces: 32767

VSCode Debugger also shows huge numbers even after assign 0 to the variables.

Obs:

• I'm using Ubuntu 20.04.
• I compiled the program with gcc version 9.3.0.
• Using zsh instead of bash (Although to use bash also does not work, just changes a little bit the huge number)

The declaration:

int c, nl, ns, nt = 0;

Only initializes nt. To initialize nl and ns as well, you need:

int c, nl = 0, ns = 0, nt = 0;