Basic beginner loop (with arrays) does NOT work but why?

Hi. I am frustrated with a piece of code I wrote because it malfunctions when the user inputs (command argument style) any string (keyword) with the letter a or A, and I have no idea why and I hate not knowing what's going on. Can you please tell me what I am doing wrong and why the code doesn't work when the user inputs a string with the letter a or A?

Code:

---

#include <cs50.h>
#include <stdio.h>
#include <string.h>

int main(int argc, string argv[])
{
    string keyword = argv[1];
    for (int j = 0; j < strlen(keyword); j++)
    {
        if (keyword[j] >= 'a' && keyword[j] <= 'z')
        {
            keyword[j] = keyword[j] - 'a';
        }
        else if (keyword[j] >= 'A' && keyword[j] <= 'Z')
        {
            keyword[j] = keyword[j] - 'A';
        }
        printf("%i\n", keyword[j]);   
    }
}

---

P.S. The code works fine with every other letter. Just not A or a.

Thank you!

It's a subtle little bug. If the string contains an 'A' or an 'a', then keyword[j] gets set to zero. Once that happens, keyword[j] = 0 = '\0' = end of string. So strlen(keyword) thinks the string ends there, and halts the loop. You want this:

Code:

---

length_of_word = strlen(keyword);
for (int j = 0; j < length_of_word; j++) {
/*and so on */

---

How does strlen() work?
What is the integer value of the character '\0'?
What is the integer value of 'a' - 'a' ?

Hi TheBigH! Thank you for your answer!

I tried putting a while loop at the bottom inside a for-loop, but it doesn't work; here's what I did:

Code:

---

printf("%i", keyword[j]);
while (keyword[j] == 0)
    j++;

---

Then, I tried writing an if-condition within the if statement:

Code:

---

for (int j = 0; j < strlen(keyword); j++)
    if (keyword[j] >= 'a' && keyword[j] <= 'z')
    {
      if (keyword[j] == 'a')
      {   
            keyword[j] = keyword[j] - 'a';
            j++;
        }
        else
            keyword[j] = keyword[j] - 'a';
    }

---

but that gives me completely different values when I enter a (it messes up the j count).

What am I doing wrong?

Quote:

---

Originally Posted by TheBigH

Code:

---

length_of_word = strlen(keyword);
for (int j = 0; j < length_of_word; j++) {
/*and so on */

---

---

Ummm.

Quote:

---

Originally Posted by Tclausex

Ummm.

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It's not exactly the answer to the question posted, but a good idea nonetheless.

Quote:

---

Originally Posted by Tclausex

How does strlen() work?

---

It counts characters until it finds one with a value zero.

Quote:

---

Originally Posted by Tclausex

What is the integer value of the character '\0'?

---

Zero.

Quote:

---

Originally Posted by Tclausex

What is the integer value of 'a' - 'a' ?

---

Seriously? You're asking this?

@Grumpy: I'm pretty sure Tclausex was asking those questions of the OP to get them thinking about the problems they were having with the code.

I'm a fan of the Socratic method /shrug.