Struc and Switch case

So, in one of my programs I have to ask the user to type in a month, and I was wondering how I can compare all the twelve months with what the user typed in. i.e. User types in: "JaNuAry", how would I compare the strings with a regular "January" and other ways to type it, also with all the other 11 months?

I was thinking something with a struc, so I can get the days in there and so that the days can't exceed beyond 31, except for February. And also using a switch case, so I can test them all out, but I have no idea how to compare both the strings from the user and from the code, and how to do it in a switch case, if possible, if there is a easier way, please let me know. Thanks a bunch

Well, for the first problem, strcmp()'ll be your best bet. Use tolower() if you like, to convert the string to lowercase.

In order to stick everything into a struct, you could go something like this:

Code:

struct date {
    unsigned day:5;
    char month[16];
}

. . . but I wouldn't. Just use ints for the dates, more like:

Code:

struct date {
    int day;
    char month[16];
}

That's assuming the months entered are never more than 15 chars long (15 + 1 for the null).

For a switch statement, in this case, it's kinda difficult I think, but you could go something like . . .

Code:

if(!strcmp(month, "january")) { /* it's january . . . */ }
else if(!strcmp(month, "february")) { /* it's february . . . */ }
/* . . . */

Note that strcmp() will return NULL if the strings are the same.

There are two distinct questions here:
1. How to compare strings, ignoring case. Many C libraries have a function called either stricmp or strcasecmp which does this. Alternatively, convert the string to all lowercase using a loop and tolower (or uppercase and toupper).

2. How to know how many days in a month, which is a bit trickier than what you describe: The months, in order from January to December have 31, 28 (29), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 days. You can do this using a switch based on month, or an array based on month, but both require that month is a number rather than a string.

--
Mats

Perhaps something like so for leap years . . .?

Code:

int monthlength[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
if(!(year % 4) && !(year % 400)) monthlength[1] = 29;

Or something similar . . .

See Wikipedia for the details on leap years, if you need to.

Changing the case of characters involves their ascii values.

Code:

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

void ToLower (char *string) {
	int i;
	for (i=0;i<strlen(string);i++) 
		if ((string[i] > 64) && (string[i] < 91)) string[i]+=32;
}

int main () {
	char this[]="jaNuaRy";
	ToLower(this);
	printf("%s\n",this);
	return 0;
}

It switches case, but sorry, there's no switch case

Originally Posted by Nightowl

Well, for the first problem, strcmp()'ll be your best bet. Use tolower() if you like, to convert the string to lowercase.

In order to stick everything into a struct, you could go something like this:

Code:

struct date {
    unsigned day:5;
    char month[16];
}

. . . but I wouldn't. Just use ints for the dates, more like:

Code:

struct date {
    int day;
    char month[16];
}

Thanks for responding quickly.

I understand what you did in the first two codes and why you chose them, the third code, i don't really undrestand the if(!strcmp). why did you use "!"? I did almost the exact same thing. Here is my struct code.

Code:

struct month{
  char monthEng[10]; //the month in english
  char monthSpan[11]; //the month in spanish
  int order; //extra, just in case...
  int numberDays; //the day of the month
};

And you said the switch case here is not really good... is there a easier way or another way around it?

Originally Posted by matsp

There are two distinct questions here:
1. How to compare strings, ignoring case. Many C libraries have a function called either stricmp or strcasecmp which does this. Alternatively, convert the string to all lowercase using a loop and tolower (or uppercase and toupper).

2. How to know how many days in a month, which is a bit trickier than what you describe: The months, in order from January to December have 31, 28 (29), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 days. You can do this using a switch based on month, or an array based on month, but both require that month is a number rather than a string.

--
Mats

Thanks for responding quickly as well. I was thinking about that, so I can just convert the months into a lowercase, which would be a lot easier. And you were talking about array based on the month, I did months[12], since there are 12 months, but the number of days in the month, how would i add that in each month? Sorry I'm very new to programming, well sort of... well yeah compared to you guys I'm like a student . But I really do have a passion for learning programming. Thanks for helping all of you, I really appreciate this.

Read what I said above . . . "Note that strcmp() will return NULL if the strings are the same.".

I mean that switch statements (for C, anyhow) won't work here very well, because you'd end up doing something like

Code:

switch(strcmp(month.monthEng, "january") {
case 0: /* They're the same . . . */ break;
default: /* They're not the same */ break;
}

switch(strcmp(month.monthEng, "february") {
case 0: /* They're the same . . . */ break;
default: /* They're not the same */ break;
}

. . . and so on. Not exactly optimal, if you get my meaning. Basically if statements, except more clunky and less readable.

Originally Posted by Nightowl

Read what I said above . . . "Note that strcmp() will return NULL if the strings are the same.".

I mean that switch statements (for C, anyhow) won't work here very well, because you'd end up doing something like

Code:

switch(strcmp(month.monthEng, "january") {
case 0: /* They're the same . . . */ break;
default: /* They're not the same */ break;
}

switch(strcmp(month.monthEng, "february") {
case 0: /* They're the same . . . */ break;
default: /* They're not the same */ break;
}

. . . and so on. Not exactly optimal, if you get my meaning. Basically if statements, except more clunky and less readable.

Ahh I see now. Hmm so I guess switch case statements here are not good.. hmm, should I just write if statements like

Code:

if(strcmp(month.monthEng, "january"))
{
    printf("You typed in %s", month.monthEng);
}
else
    printf("Please type in all lower case");

Something like that?

Yes, but you'll want something more like

Code:

if(!strcmp(month.monthEnd, "january")) printf("You typed in january.\n");
else if(!strcmp(month.monthEnd, "february")) printf("You typed in february.\n");
/* . . . */
else {printf("Please type the month in all lowercase.\n");

. . . in all likelihood. What you typed won't work for *any* months other than January.

EDIT: Note the ! before the strcmp() . . . it's required. strcmp() will return NULL if the strings match, and since you're checking for a match, you want to actually check for a NULL.

Originally Posted by Nightowl

Yes, but you'll want something more like

Code:

if(!strcmp(month.monthEnd, "january")) printf("You typed in january.\n");
else if(!strcmp(month.monthEnd, "february")) printf("You typed in february.\n");
/* . . . */
else {printf("Please type the month in all lowercase.\n");

. . . in all likelihood. What you typed won't work for *any* months other than January.

EDIT: Note the ! before the strcmp() . . . it's required. strcmp() will return NULL if the strings match, and since you're checking for a match, you want to actually check for a NULL.

OoO I see what your saying, do the if, else if ... (continuing until december), and then at the end do the else to finalize to type in lower case. I understand now.

hmm, i was just wondering, are we able to compare 3 strings with each other? Like, the one from the user, month in english and month in spanish? Or is this totally different?

Originally Posted by dlwlsdn

Ahh I see now. Hmm so I guess switch case statements here are not good.. hmm, should I just write if statements like

Code:

if(strcmp(month.monthEng, "january"))
{
    printf("You typed in %s", month.monthEng);
}
else
    printf("Please type in all lower case");

Something like that?

You might as well convert to numbers using an array, then a for loop which checks against the numbers. If you use a global const char array (month[0]=january, etc.) and two short functions (one which accepts a char* and returns an int, and one which accepts an int and returns a char*) the conversion will be quick and painless both ways. That makes the for loop pretty simple too.

Originally Posted by MK27

You might as well convert to numbers using an array, then a for loop which checks against the numbers. If you use a global const char array (month[0]=january, etc.) and two short functions (one which accepts a char* and returns an int, and one which accepts an int and returns a char*) the conversion will be quick and painless both ways. That makes the for loop pretty simple too.

Very good point.

Something like . . .

Code:

const char monthchars[12][] = {"january", "february", "march", "april", "may", "june", "july", "august", "september", "october", "november", "december"};

int get_month_as_int(char *monthstr) { /* could also pass your struct into here . . . */
    if(!strcmp(monthstr, monthchars[0])) return 0;
    if(!strcmp(monthstr, monthchars[1])) return 1;
    if(!strcmp(monthstr, monthchars[2])) return 2;
    /* or make this into a for() loop . . . simpler, like so . . . */
    for(x = 0; x < 12; x ++) {
        if(!strcmp(monthstr, monthchars[x])) return x;
    }
    printf("Please type the month in lowercase . . .\n");
    return -1;
}

char *get_month_as_str(int monthint) {
    return months[monthint]; /* check that monthint is >= 0 && < 12 . . . */
}

Remember to experiment . . . can't go wrong, unless you don't make a backup beforehand.

Originally Posted by MK27

You might as well convert to numbers using an array, then a for loop which checks against the numbers. If you use a global const char array (month[0]=january, etc.) and two short functions (one which accepts a char* and returns an int, and one which accepts an int and returns a char*) the conversion will be quick and painless both ways. That makes the for loop pretty simple too.

Thanks for the insight. I'll try rewriting this program again, in different ways, I think thats the best way to learn as well. But right now, i want to get used to structs and strings. But thats a great way of doing this, I wouldn't have thought of that in like ages. But you were saying char* and returns a int. Is that even possible? I was reading the online lesson on cprogramming.com, I can't recall anything about a char* returning a int, would be something like

Code:

month[0] = "january";
month[1] = "february";
// .....
char *pointer1;
int i=0, x;

for(i=0;i<11;i++)
{
     x = *(pointer1 + i);
}

return x;

Or am I totally off on my pointers? I really appreciate your help though, you guys are awesome ^^, seriously.

Originally Posted by Nightowl

Very good point.

Something like . . .

Code:

const char monthchars[12][] = {"january", "february", "march", "april", "may", "june", "july", "august", "september", "october", "november", "december"};

int get_month_as_int(char *monthstr) { /* could also pass your struct into here . . . */
    if(!strcmp(monthstr, monthchars[0])) return 0;
    if(!strcmp(monthstr, monthchars[1])) return 1;
    if(!strcmp(monthstr, monthchars[2])) return 2;
    /* or make this into a for() loop . . . simpler, like so . . . */
    for(x = 0; x < 12; x ++) {
        if(!strcmp(monthstr, monthchars[x])) return x;
    }
    printf("Please type the month in lowercase . . .\n");
    return -1;
}

char *get_month_as_str(int monthint) {
    return months[monthint]; /* check that monthint is >= 0 && < 12 . . . */
}

Remember to experiment . . . can't go wrong, unless you don't make a backup beforehand.

const char monthschar[12][], why did you do a 2-dimension... I don't know 2-dimensions at all, or when to use them. haha, but i understand everything you wrote, except the 2-dimensions. Is it cause we are making it 12 elements long, and each element will have, the months you wrote?