C programming: print only int from fgets

Question

See this main:

int main(void)
{
    int i;
    int ch;
    char str[512];
    fgets(str, sizeof str, stdin);

    for (i = 0; i <= (strlen(str)); i++)
    {
        if (str[i] != '\0' && str[i] != '\n')
        {
            int num = atoi(&str[i]);
            printf("%d\n", num);
        }
    }

    return 0;
}

I want to get line with numbers from user and get all the numbers without any spaces or tabs.

For example:

The input 1 2 3. But in this case this the output:

1
2
2
3
3

So why i received 2 and 3 twice?

Answer 1

Here's how I would do it:

char line[256];
if (fgets(line, sizeof line, stdin) != NULL)
{
    const char *ptr = line;
    while (*ptr != '\0')
    {
        char *eptr = NULL;
        const long value = strtol(ptr, &eptr, 10);
        if (eptr != ptr)
            printf("%ld\n", value);
        else
            break;
        ptr = eptr;
    }
}

This uses strtol() so it will also handle negative numbers; if this is incorrect you can of course add checks to filter them out. I think this is way better than anything using strtok().

Answer 2

Because the you also pass the position of the string which starts with spaces. they get the first number to be 2 and 3 respectively twice. That is what is returned.

for (i = 0; i <= (strlen(str)); i++)
{
    if (str[i] != '\0' && !isspace(str[i]) )
    {
        int num = atoi(&str[i]);
        printf("%d\n", num);
    }
}

Prints:

1
2
3

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^{For the purpose of tokenizing you can use strtok and to convert it to number strtol etc. These provides much better control over the error cases than atol/atoi do.}