Logical Error With Type Conversion In C

So, I'm into about 650 lines of some code I'm working on. So I'll try to explain instead of flooding this post. Say I have some code like this:

int main() {
    int i, j;
    char data[INPUT_BUFF];

    printf("Gimme something: ");
    fgets(data, INPUT_BUFF, stdin);

    for (j = 0; j < data[INPUT_BUFF]; j++){
    switch(data[j]){
    case 0: 
        if(j == 'e'){
            atoi(data);
            data[j] = ranit(e_array);
            sprintf( data, "%d", data );
        }
    case 1: 
        if(j == 'm'){
            atoi(data);
            data[j] = ranit(m_array);
            sprintf( data, "%d", data );
        }
    case 2: 
        if(j == 'n'){
            atoi(data);
            data[j] = ranit(n_array);
            sprintf( data, "%d", data );
        }
    case 3: 
        if(j == 'o'){
            atoi(data);
            data[j] = ranit(o_array);
            sprintf( data, "%d", data );
        }
    case 4: 
        if(j == 'y'){
            atoi(data);
            data[j] = ranit(y_array);
            sprintf( data, "%d", data );
        }

     }
     }

     for (i = 0; i < INPUT_BUFF; i++){
         printf("%x\n", (int)data[(int)i]);
     }

     return 0;
}

I have a switch statement in the above that only checks for the characters in the word 'money'. The entire alphabet would have been too much to put here. The function ranit() grabs a random element out of the array it is past. That function has been checked and works perfect. In the case all the elements are numbers. I've tried to do this a lot of different ways, but what I want to do is after checking for a matching character, replace it with a random element in from the corresponding arrays that contain integers.

I tried using atoi() to make the 'data' character array able to hold integers. That way I wouldn't get an error about mismatching types. At some point I could have sworn itoa worked with gcc, but I now see this is no longer part of the standard library. I tried using sprintf() to convert the data array back to chars for the next iteration of the loop.

When I run the code I notice the random numbers aren't displayed, but the hex equivalents for the ascii values of the word 'money':

$ ./test 
Gimme something: money
6d
6f
6e
65
79

I'm unsure if I'm assigning the values wrong or if sprintf won't allow for the same source and destination values. All the examples I found would put this in a new variable or array name, but I need to have it in the same for the next loop iteration. So maybe I should be using something else?

No warnings or errors from the compiler. Just strictly a logical error at this point. Any suggestions much appreciated.

for (j = 0; j < data[INPUT_BUFF]; j++){

This is wrong.

for (j = 0; data[j] != 0; j++){

This is probably what you want.

switch(data[j]){
    case 0: 
    ...
    case 1:
    ...
    case 2:
    ...

This is wrong.

switch(data[j]){
    case 'm':
    ...
    case 'o':
    ...
    case 'n':
    ...
    case 'e':
    ...

This might be more like what you want... Maybe. I don't really understand your train of thought.

atoi(data);

This is wrong. It does absolutely nothing at all.

data[j] = ranit(m_array);

This might be wrong. What is m_array?

Very odd. I had tried using letters in place of the numbers I had in the switch/case before, but I could not get it to work. Now it works with the exert I provided earlier. I didn't show in that exert, but I also included digits, letters and special characters with the rest of the code. Perhaps I just didn't escape some special character properly, but I can come back to that later.

If I print out the m_array with something like this:

for (i = 0; i < DATA_SIZE; i++){
            printf("%x\n", m_array);
    }

I get back an array of random numbers that I generated from another function:

 ./test | tail 
8885ffc9
77a822d5
bf34d05d
bc229af3
fc171fb9
ab7d3609
4815ef59
83facdc3
7d77bf58
881d17ea

Then I have another function that should randomly select an element from that array, or for any of the arrays from characters that match, and use one number to replace the letter given. Sorry if that wasn't clear.

With using the characters in the switch/case I guess the whole conversion of char arrays to ints won't be needed. I could just create a new array with the numbers that are switched for the letters I guess.

I'm sure you're right about this part, but I'd like to understand why:

data[j] = ranit(m_array);

That function should just grab one random element that's a number from the m_array. I guess I'm assigning it wrong there?

Single and double quotes are very different things in C. In C, "A" means a string -- amounting to the array { 'A', '\0' }. And 'A' is just the number 65.

Numbers that large won't fit in your input array. chars are numbers, but their range is only -128 through +127. It'll work fine if you use a separate array of type 'int' output.

The POSIX standard requires that type char in the C language must be an 8-bit type. The C Standard doesn't specify whether type char is signed or unsigned. So the range of values that can be contained in a char is [-128, 127] on some POSIX conforming systems and [0, 255] on others.

On non-POSIX systems, the C standard allows the type char to be wider than 8 bits. On systems that use UTF-16 as the codeset underlying their system character sets, a char would likely be 16-bits wide.

Thanks for correcting my too-specific answer. 16 bits is still too small for his numbers, be they signed or unsigned, so the point stands however.

Thank you both for explaining why this would not work. At one time I new about the char range, but forgot. Much appreciated again!