Comparing integer char[] elements

Hey everybody,

I've got two char arrays which each represent college course names. I want to compare the courses based off the integer part of their name to determine which one is larger, but am not quite sure how to do this. These are the two arrays I've got...

Code:

---

char a[6] = "CS120";
char b[6] = "CS450";

---

I am trying to accomplish this:

Code:

---

if(120 < 450)
{
    do stuff here
}

---

Any help or suggestions would be greatly appreciated.

Thanks,
Chris C.

1. Find where the number starts.
2. Use strtol or atoi to turn the rest of the string into an integer.

Of course, tabstops reply applies if you actually need to know what the number is.

If you just compare the strings (using for example strcmp), then "CS120" will be less than "CS450" (strcmp will return a number less than zero if the first string is "less" than the second string are in that order).

--
Mats

You could use strcmp(). strcmp will tell you that CS120 comes before CS450 by returning a negative number (or maybe positive- look up the specs for yourself.)
example:

Code:

---

if (strcmp(a,b)<0) /* Just like if (a<b) */
{
    stuff
}

---

Ok, that makes sense. So I would just need to isolate the number part (i.e. indexes 2-4) of the string and pass that into the atoi() function.

Is there a easy way to isolate a substring of a string, or would I just need to copy the values to a new string? Something like this:

Code:

---

char a[6] = "CS120";
char newarray[4];

newarray[0] = a[2];
newarray[1] = a[3];
newarray[2] = a[4];

---

Thanks,
Chris C.

If you Know that it's always 2 chars to begin with (such as "CS", "AA", "XY" etc), and that the number fills the entire rest of the string, then you could use atoi like this:

Code:

---

int n = atoi(&str[2]);

---

Although I would prefer something that uses strtol(), since strtol() is more able to cope with malformed inputs and give you a chance of detecting this - atoi() is very bad at coping with malformed input, and will not tell you at all that it failed, or why...

--
Mats

atoi requires a pointer to the start of the string, which in your case would be &a[2] (or a+2 if you like the pointer arithmetic).

Ok, thanks guys. I'll give strcmp() a try first. That sounds like it might work... if not, I'll go the atoi() route.

Thanks,
Chris C.