Why are there garbled characters in this C program output?

#include <stdio.h>
#include <locale.h>
#include <wchar.h>

int main() {
//    setlocale("LC_ALL","");
    unsigned char utf[]={0xe4,0xb8,0x80,0x0a};
    printf("%s",utf);
    return 0;
}

• The first four bytes of output are correct. The second line in the console is not expected

Your array is missing the null terminator strings require, so printf keeps on printing bytes beyond the end of the array until it happens upon a null byte. (Or when your program crashes due to an out of bounds access.)

Add the null byte:

unsigned char utf[]={0xe4,0xb8,0x80,0x0a,0x00};