C question with strings

[hakermania]

Hi, I would like to ask you how do strings work...
I have made this program:

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

int main()
{
int a, s2;
char s1[256];
char s3[256];
printf(" Choose what do you wanna do:\n 1=Answer to a retorical question\n2=Answer to a mathematical question\n 3=Answer to a computer's question\n:");
scanf("%d",&a);
if (a == 1);
{printf("Na zei kaneis h' na mhn zei?\n");
scanf("%c",s1);
if (s1 = "na zei");
printf("Kai gt na zei parakalw?\n");
else if (s1 = "na mhn zei" );
printf("Psofos!!!\n");
else printf(" ERROR\n\n");}
else if (a = "2");
{printf("Poso mas kanei 2 + 2?\n");
scanf("%d",s2);
if (s2 = 4);
printf("Swsta\n");
else printf("La8os\n");}
else if (a = "3");
{printf("Geia, eimai to pc su.Me exeis talaipwreisei poly! To 3ereis?\n");
scanf("%c",s3);
if (s3 = "3erw" );
printf("Pali kala, gt mu exeis bgalei thn pisth!!!\n");
else if (s3 = "den 3erw" )
printf("kala 8a kaneis na ma8eis!\n");
else printf("Eimai to pc su kai den katalaba ti mu apanthses!!!\n");}
else printf("Den edwses ute 1 ute 2 ute 3.3anaprospa8hse se parakalw!\n");

return ;
}
Em......I know that does not work at all.
Can you please tell me how is this supposed to work?:confused:??

[JDShu]

First thing that jumps out to me is that for comparisons, use "==" not "=". You're assigning in the if statement when you're supposed to be comparing.

EDIT: ok.. I just realized there more than that... you ended your if statements prematurely, a is an integer when you're comparing it to a string, and you can't compare strings in the first place in C. You need to use strcmp() or something.

[Barrucadu]

You can't check for string equality like that, you have to use strcmp() (or strncmp()).

And what's with all the extra semicolons? (eg: "if (s1 = "na zei");")

[Xyro]

scanf("%c",s1);

This reads in a single character, not a string. You want:

scanf("%s",s1);

Since this is not safe, you should avoid using scanf(). However, for learning it is fine. No one will hack your system and perform a buffer overflow attack with your test program...

Edit:

...And what's with all the extra semicolons? (eg: "if (s1 = "na zei");")

Yea, you've got a whole swack of extra semicolons and unbalanced parenthesis. Remember, if you open it '(,{,[' you've gotta close it '),},]'.


Try this: (may have errors, did a quick once over for obvious mistakes...)



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

int main()
{
int a, s2;
char s1[256];
char s3[256];
printf(" Choose what do you wanna do:\n 1=Answer to a retorical question\n2=Answer to a mathematical question\n 3=Answer to a computer's question\n:");
scanf("%d",&a);
if (a == 1) {
printf("Na zei kaneis h' na mhn zei?\n");
scanf("%s",s1);
if ( strcmp(s1, "na zei") == 0 )
printf("Kai gt na zei parakalw?\n");
else if ( strcmp( s1, "na mhn zei") == 0 )
printf("Psofos!!!\n");
else
printf(" ERROR\n\n");
}
else if (a == 2) {
printf("Poso mas kanei 2 + 2?\n");
scanf("%d",&s2);
if (s2 == 4)
printf("Swsta\n");
else
printf("La8os\n");
}
else if (a == 3) {
printf("Geia, eimai to pc su.Me exeis talaipwreisei poly! To 3ereis?\n");
scanf("%s",s3);
if ( strcmp(s3, "3erw") == 0 );
printf("Pali kala, gt mu exeis bgalei thn pisth!!!\n");
else if ( strcmp(s3, "den 3erw") == 0 )
printf("kala 8a kaneis na ma8eis!\n");
else
printf("Eimai to pc su kai den katalaba ti mu apanthses!!!\n");
}
else printf("Den edwses ute 1 ute 2 ute 3.3anaprospa8hse se parakalw!\n");

return 0;
}

[Some Penguin]

Hi, I would like to ask you how do strings work...
I have made this program:

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

int main()
{
int a, s2;
char s1[256];
char s3[256];


Your life will be easier if you develop good habits re: variable naming.

If you were reading code and s1 and s3 were declared as character arrays of one particular size, would you expect s2 to be an integer? Probably not...




printf(" Choose what do you wanna do:\n 1=Answer to a retorical question\n2=Answer to a mathematical question\n 3=Answer to a computer's question\n:");
scanf("%d",&a);


Something to consider: inputs that aren't numbers.




if (a == 1);


This isn't Bourne shell. That semicolon is not only unnecessary, it leads to behavior radically different than what you want.

Vaguely related recommendation: add -Wall to your compilation flags. Read the warnings. Look them up and understand them.




{printf("Na zei kaneis h' na mhn zei?\n");
scanf("%c",s1);
if (s1 = "na zei");


-Wall would have told you that you shouldn't do that.

strncmp, stricmp, strcasecmp...

Etc.

[hakermania]

All in all what I wanna do is to check the user's answer and then if he/she answered the one thing to do this and if he/she answer the other thing to do the other.how do I "compare" strings? Em...How do I use strcmp() and strncmp()?And what could I use except of scanf?

[MadCow108]

manpages are your friend (if you installed devhelp)
man strcmp
man strncmp



if (strncmp(string1, string2, max_length_to_compare) == 0)
{
printf("zero means equal")
}


instead of using scanf, you can write your own function parsing your input
if that makes any sense depends on the problem, often scanf is the way to go.

[dwhitney67]

For reading strings from the user, fgets() is preferred versus scanf().

fgets() permits the programmer to specify the maximum bytes to read from stdin, thus mitigating the overrunning of a buffer.

Example:


char input[80];

printf("Enter something: ";
fgets(input, sizeof(input), stdin);

/* NOTE: fgets() may insert a newline character into the
buffer. You will have to remove this character
should its presence not be desired/required.

fgets() will always null-terminate the buffer.
*/

/* to remove the a newline character from the buffer */
char *nl = strchr(input, '\n');

if (nl) { *nl = '\0'; }

Read the manpage for fgets() for more details.

[hakermania]

Guys, I have to say that you do great work here! I understood everything.Thank you thank you and thank you