Question

I found several answers to this in C++ or C#, but none for C.

I need to know how to count the number of characters in a string. The goal is to determine whether there is a closed block (bounded by braces '{', '}') in a string. right now I have the following:

int closedBlock(char* value) {
    int open = 0;

    int i;
    for (i = 0; i < strlen(value); i++) {
        if (!strcmp("{", value[i])) {
            open++;
        } else if (!strcmp("}", value[i])) {
            open--;
        }
    }

    return !open;
}

but it crashes after on the first if check. I’m not really clear on why this does not work. I imagine it has something to do with bad pointers (that seems to always be the problem in C), but I can’t figure it out. In addition to working code, and explanation of why mine is bad would be greatly helpful.

Thanks.

NOTE

I am aware that this simply check that the number of '{' is equal to the number of '}', and not truly that there is a properly closed block. I’ll solve that problem after I solve this one.

Answer 1

strcmp will compare two null-terminated strings. It still baffles me that your compiler actually doesn’t mutter about the second parameter being a char. If you want to compare a single character just use the equal-operator ==:

int closedBlock(char* value) {
    int open = 0;
    int length = strlen(value);
    int i;
    for (i = 0; i < length; i++) {
        if (value[i] == '{') {
            open++;
        } else if (value[i] == '}') {
            open--;
        }
    }

    return !open;
}

Hint: If you work with gcc add -Wall -Wextra to your compiler call, it will often result in useful warnings.

I am aware that this simply check that the number of ‘{‘ is equal to the number of ‘}’, and not truly that there is a properly closed block. I’ll solve that problem after I solve this one.

Another hint here: when can there be an invalid block? If and only if the end-token } occurs without a preceding start-token {. You already have all tools for this, you’re just missing another if-statement.