Print character + the ASCII value, 10 pairs per line My exercise was:


  Write a program that reads input as a stream of characters until encountering
  EOF. Have the program print each input character and its ASCII decimal value.
  Note that characters preceding the space character in the ASCII sequence are
  nonprinting characters. Treat them specially. If the nonprinting character is a
  newline or tab, print \n or \t, respectively.
  Print 10 pairs per line, except start a fresh line each time a newline character is encountered.


This is my code (regarding the special characters, I defined only \n and \t):

#include &lt;stdio.h&gt;
int special_chars(int ch);

int main(void)

{
    int x;
    printf("please enter a some characters, and ctrl + d to quit\n");

    special_chars(x);

    return 0;
}

int special_chars(int ch)

{
    int pairsNum = 0;

    while ((ch = getchar()) != EOF)// testing charecters while not end of file.
    {

    if (ch == '\n')// testing if a control charecter, and printing its
     {
        printf("\\n ");
        pairsNum++;
     }

    else if (ch == '\t')
     {
        printf("\\t ");
        pairsNum++;
     }

    else
    {
        printf("%c,%d ", ch, ch);
        pairsNum++;
    }

    if (pairsNum == 10)// counting the number of outputs, and printing a newline when is 10 (limit).
        printf("\n");
    }
    return ch;
}
A few issues, in no particular order:


put main last to avoid the need for a prototype.
main normally takes argc/argv parameters
special_chars should be static - but it is debateable whether a separate
function is necessary in a short program like this.
main defines variable x and passes it to special_chars.  This is
unnecessary. Just define ch in special_chars and define the function as
taking void (i.e. nothing)
why does special_chars return a value?
indenting is wrong
too many blank lines (8)
missing {} brackets after if (pairsNum == 10)
mixed naming styles (pairsNum should be pairs_num or special_chars should
be specialChars - I prefer the former)
special_chars is a bad name for the function.
pairsNum is an odd name; n_pairs would be my choice.
you don't print a final \n at the end of the program 
you don't start a new line after reading a \n, as required - it appears that you do    when you type at the keyboard because entering a \n causes a new line. But if you redirect input into your program it
does not.  Also you don't start a line after each ten, only after the first ten. e.g. if your program executable is called program

$ cat x
abcdefgh
ijklmnop
qrstuvwxyz

$./program &lt; x
please enter a some characters, and ctrl + d to quit
a,97 b,98 c,99 d,100 e,101 f,102 g,103 h,104 \n i,105 
j,106 k,107 l,108 m,109 n,110 o,111 p,112 \n q,113 r,114 s,115 t,116 u,117 v,118 w,119 x,120 y,121 z,122 \n $