Why doesn't my character counter work properly?

Question

I recently started to learn C language and I'm currently trying to code a simple program which should return the number of times that a character has been used, but the output is wrong. Why doesn't it work properly? Any help will be really appreciated. Here's the code:

#include <stdio.h>

main() {
    int c, i;
    int ndigit[25]; //a = 97

    while( (c = getchar()) != EOF) {    
        ++ndigit[c - 97];
    }
    
    for (i = 0; i < 26; i++) {  
        putchar(i + 97);
        printf(" = %d\n", ndigit[i]);
    }
}

And here's the output with the word "hello":

a = 8
b = 0
c = 4203649
d = 0
e = 4202641
f = 0
g = 84
h = 1
i = 12260176
j = 0
k = 1
l = 2
m = -1
n = -1
o = 85
p = 0
q = 1
r = 0
s = 4203673
t = 0
u = 0
v = 0
w = 84
x = 0
y = 0
z = 0

Answer 1

When you make a new array it might contain random numbers. You need to manually set it to 0s. A way to do that is use the following function:

memset(ndigit,0,sizeof(int)*26);

You also need to include string.h to use that

Edit: Forgot that the array is type int so we need to multiply the size by the size of an int

Edit2: Also i think you want your array to have size 26

Answer 2

Your problem is that your array may contain random values. In C/C++ you are not guarantied that memory is zeroed out at the start of the program, but rather you might get whatever was there before. As above stated you could use some built in function, but simply doing this:

int ndigit[26]; // as mentioned in comments and in previous answers English alphabet has 26 characters

for (int i = 0; i < 26; ++i)
   ndigit[i] = 0;

// rest of you code here

One more problem is in main you have to put return 0 for same reason as your array. Random value could be returned if you do not have return 0.

main () {
   // your code here

   return 0;
}

Per @superior you could also use

ndigit[26] = {0}

This is however C99 standard and come compilers which do not follow it strictly will not initialize array. I know gcc version prior to 4.xx did not.

EDIT: Here is my output with your (OP's code) with inputhello

a = 4543
b = 0
c = 0
d = 0
e = 1318238529
f = 32604
g = 121
h = 1
i = 37
j = 57
k = 1136
l = 2
m = 1
n = 0
o = 4195998
p = 0
q = 142
r = 0
s = 0
t = 0
u = 4195920
v = 0
w = 4195568
x = 0
y = -1400909520
z = 32767

Here is output of my answer, with for() loop, and suggested {0}.

a = 0
b = 0
c = 0
d = 0
e = 1
f = 0
g = 0
h = 1
i = 0
j = 0
k = 0
l = 2
m = 0
n = 0
o = 1
p = 0
q = 0
r = 0
s = 0
t = 0
u = 0
v = 0
w = 0
x = 0
y = 0
z = 0

Answer 3

I'm currently trying to code a simple program which should return the number of times that a character has been used

That's a rather good starter exercise.

Some notes that will make it easier to get to results faster:

• Use your compiler's ability to help you
  • If you are using gcc or clang: -stdc18 -Wall -Wextra -pedantic -pedantic-errors

What you will notice is that wour main() function is invalid. C doesn't allow type-less functions. A proper main needs to be returning int, implicitly or explicitly. If in doubt, just know that it will return 0 by default.

You also not initialize your array. That has consequences - like not nowing what will happen when reading from the memory.

---

A suggestion to fix the program is not to use magic numbers. It is a trap (assuming 97 will fall out of fashion long before 'a' will). Use 'a' - or better, use the constants in the C library.

Everything below here goes awry once unicode comes into play but it counts "bytes" values well.

#include <stdio.h>
#include <string.h>
#include <limits.h> /* UCHAR_MAX (almost never anything but 255) */

char friendlify(unsigned char x) { /* unsigned to char cast ... */
    /* this is just for presentation - purely ASCII friendly */
    /* ternary operator: (condition) ? (true) : (false) */
    return x < '.' || x > '~' ? '.' : x;
}

int main() {
    int c;
    /* make room for all `char`s (unsigned chars really) */
    unsigned ndigit[UCHAR_MAX+1] = {0}; /* zero initialize */

    while ((c = getchar()) != EOF) {
        /* since getchar returns an unsigned - (unless EOF) we're not worried here) */
        ++ndigit[c];
    }

    printf("Collected:\n");
    for (unsigned i = 0; i <= UCHAR_MAX ; ++i) {
        /* just print characters included in the input */
        if (ndigit[i]) { /* assuming zero hits aren't interesting */

            /* %02X and the `i` makes it print the hex value of that particular byte */
            printf("0x%02X  %c  Count = %u\n", i, friendlify(i), ndigit[i]);
        }
    }
}