Random characters printed after printing 'result'

Question

I'm getting random characters after the actual output in printf("%s",result);. Why are these characters being printed? And how can I remove them?

#include<stdio.h>
char *replacechar(char[]);

int main()
{
    char str[25];
    char *result;
    int i=0;
    while( (str[i++]=getchar()) != '\n' && i < 25);
    result= replacechar(str);
    printf("%s",result);
    return 0;
}

char *replacechar(char str[])
{
    return str;
}

Expected Output:

aaayt
aaayt

Actual Output:

aaayt
aaayt
↑@

Answer 1

For starters the operands of the condition

(str[i++]=getchar()) != '\n' && i < 25

should be swapped.

i < 25 && (str[i++]=getchar()) != '\n'

The input stored in the character array str should be zero-terminated. Otherwise the array will not contain a string.

Here is a demonstrative program that shows how your code can be rewritten

#include <stdio.h>

char *replacechar( char str[] )
{
    return str;
}

int main(void) 
{
    enum { N = 25 };
    char str[N];
    char *result;

    size_t i = 0;

    while( i < N - 1 && ( str[i] = getchar() ) != '\n' ) i++;

    str[i] = '\0';

    result = replacechar( str );

    puts( result ); 

    return 0;
}

Its output might look like

Hello Siddharth Awana
Hello Siddharth Awana