strcmp() not returning what it should return
-3
Basically I want to create a program that would have potential questions that might be in my upcoming exam in Digital Systems.
#include <stdio.h>
#include <string.h>
int main() {
char input1[600];
printf("What is the set of available registers?");
scanf("%s", &input1);
if(strcmp(input1, "registers, memory, hard disc") == 0){
printf("Good job! You got it right");
}
else {
printf("Wrong answer!");
}
So whenever I type "registers, memory, hard disc" when I'm asked it returns 1 instead of 0. I cannot see the problem. I am kind of new to C so sorry if it is a silly question.
c string string-comparison strcmp
edited Nov 25 '18 at 18:29
alk
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
|
show 1 more comment
-3
Basically I want to create a program that would have potential questions that might be in my upcoming exam in Digital Systems.
#include <stdio.h>
#include <string.h>
int main() {
char input1[600];
printf("What is the set of available registers?");
scanf("%s", &input1);
if(strcmp(input1, "registers, memory, hard disc") == 0){
printf("Good job! You got it right");
}
else {
printf("Wrong answer!");
}
So whenever I type "registers, memory, hard disc" when I'm asked it returns 1 instead of 0. I cannot see the problem. I am kind of new to C so sorry if it is a silly question.
c string string-comparison strcmp
edited Nov 25 '18 at 18:29
alk
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
usefgetsto read a line that contains spaces.strcspncan be used to remove the trailing newline.
– xing
Nov 25 '18 at 17:41
3
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
1
scanffamously (yes; it is by design) separates input on spaces.
– usr2564301
Nov 25 '18 at 17:43
5
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
1
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51
|
show 1 more comment
-3
-3
-3
Basically I want to create a program that would have potential questions that might be in my upcoming exam in Digital Systems.
#include <stdio.h>
#include <string.h>
int main() {
char input1[600];
printf("What is the set of available registers?");
scanf("%s", &input1);
if(strcmp(input1, "registers, memory, hard disc") == 0){
printf("Good job! You got it right");
}
else {
printf("Wrong answer!");
}
So whenever I type "registers, memory, hard disc" when I'm asked it returns 1 instead of 0. I cannot see the problem. I am kind of new to C so sorry if it is a silly question.
c string string-comparison strcmp
edited Nov 25 '18 at 18:29
alk
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
Basically I want to create a program that would have potential questions that might be in my upcoming exam in Digital Systems.
#include <stdio.h>
#include <string.h>
int main() {
char input1[600];
printf("What is the set of available registers?");
scanf("%s", &input1);
if(strcmp(input1, "registers, memory, hard disc") == 0){
printf("Good job! You got it right");
}
else {
printf("Wrong answer!");
}
So whenever I type "registers, memory, hard disc" when I'm asked it returns 1 instead of 0. I cannot see the problem. I am kind of new to C so sorry if it is a silly question.
c string string-comparison strcmp
c string string-comparison strcmp
edited Nov 25 '18 at 18:29
alk
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
edited Nov 25 '18 at 18:29
alk
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
edited Nov 25 '18 at 18:29
alk
59.1k765179
edited Nov 25 '18 at 18:29
alk
59.1k765179
edited Nov 25 '18 at 18:29
alk
59.1k765179
59.1k765179
asked Nov 25 '18 at 17:39
dangerardangerar
112
asked Nov 25 '18 at 17:39
dangerardangerar
112
asked Nov 25 '18 at 17:39
dangerardangerar
112
112
usefgetsto read a line that contains spaces.strcspncan be used to remove the trailing newline.
– xing
Nov 25 '18 at 17:41
3
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
1
scanffamously (yes; it is by design) separates input on spaces.
– usr2564301
Nov 25 '18 at 17:43
5
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
1
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51
|
show 1 more comment
usefgetsto read a line that contains spaces.strcspncan be used to remove the trailing newline.
– xing
Nov 25 '18 at 17:41
3
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
1
scanffamously (yes; it is by design) separates input on spaces.
– usr2564301
Nov 25 '18 at 17:43
5
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
1
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51
use
fgets to read a line that contains spaces. strcspn can be used to remove the trailing newline.Nov 25 '18 at 17:41
use
fgets to read a line that contains spaces. strcspn can be used to remove the trailing newline.Nov 25 '18 at 17:41
3
3
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
1
1
scanf famously (yes; it is by design) separates input on spaces.– usr2564301
Nov 25 '18 at 17:43
scanf famously (yes; it is by design) separates input on spaces.– usr2564301
Nov 25 '18 at 17:43
5
5
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
1
1
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51
|
show 1 more comment
3 Answers
3
active
oldest
votes
2
As already said in the comments, scanf() with "%s" stops conversion at the first whitespace character. To read a whole line of text, use fgets():
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// ...
char foo[100];
if(!fgets(foo, sizeof(foo), stdin)) // don't use sizeof on pointers
; // handle error // for that purpose!
size_t length = strlen(foo);
if(length && foo[length - 1] == 'n') // fgets also reads the newline character
foo[--length] = ''; // at the end of the line, this removes it.
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
Good use offgets()and good test to prevent hacker exploit of entering a null character as the first character.
– chux
Nov 25 '18 at 20:52
Nice one.fgetsis of course preferable, but I added an answer on how to do withscanf
– Broman
Nov 25 '18 at 22:36
add a comment |
1
Swordfish has already given a good answer, and fgets is preferable to scanf. However, I want to show how you would use scanf in this case:
if(scanf("%599[^n]", input1) != 1) {
// Handle error
}
So what is different?
scanfreturns the number of successfully assignments, so if this returns 1, theninput1has been assigned. If not, an error has occured.- Changed
sto[^n]to read until newline - Inserted
599(one less than 600) so ensure that we don't write outside the array. - Removed
&frominput1. In this case, it would probably work anyway, but it is undefined behavior, which should be avoided at all costs.
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
add a comment |
-2
Try change your scanf line from:
scanf("%s", &input1);
to:
scanf("%[^n]", input1);
It worked out for me.
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
2
As already said in the comments, scanf() with "%s" stops conversion at the first whitespace character. To read a whole line of text, use fgets():
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// ...
char foo[100];
if(!fgets(foo, sizeof(foo), stdin)) // don't use sizeof on pointers
; // handle error // for that purpose!
size_t length = strlen(foo);
if(length && foo[length - 1] == 'n') // fgets also reads the newline character
foo[--length] = ''; // at the end of the line, this removes it.
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
Good use offgets()and good test to prevent hacker exploit of entering a null character as the first character.
– chux
Nov 25 '18 at 20:52
Nice one.fgetsis of course preferable, but I added an answer on how to do withscanf
– Broman
Nov 25 '18 at 22:36
add a comment |
2
As already said in the comments, scanf() with "%s" stops conversion at the first whitespace character. To read a whole line of text, use fgets():
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// ...
char foo[100];
if(!fgets(foo, sizeof(foo), stdin)) // don't use sizeof on pointers
; // handle error // for that purpose!
size_t length = strlen(foo);
if(length && foo[length - 1] == 'n') // fgets also reads the newline character
foo[--length] = ''; // at the end of the line, this removes it.
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
Good use offgets()and good test to prevent hacker exploit of entering a null character as the first character.
– chux
Nov 25 '18 at 20:52
Nice one.fgetsis of course preferable, but I added an answer on how to do withscanf
– Broman
Nov 25 '18 at 22:36
add a comment |
2
2
2
As already said in the comments, scanf() with "%s" stops conversion at the first whitespace character. To read a whole line of text, use fgets():
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// ...
char foo[100];
if(!fgets(foo, sizeof(foo), stdin)) // don't use sizeof on pointers
; // handle error // for that purpose!
size_t length = strlen(foo);
if(length && foo[length - 1] == 'n') // fgets also reads the newline character
foo[--length] = ''; // at the end of the line, this removes it.
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
As already said in the comments, scanf() with "%s" stops conversion at the first whitespace character. To read a whole line of text, use fgets():
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// ...
char foo[100];
if(!fgets(foo, sizeof(foo), stdin)) // don't use sizeof on pointers
; // handle error // for that purpose!
size_t length = strlen(foo);
if(length && foo[length - 1] == 'n') // fgets also reads the newline character
foo[--length] = ''; // at the end of the line, this removes it.
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
edited Nov 25 '18 at 21:11
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
answered Nov 25 '18 at 17:53
SwordfishSwordfish
1
1
Good use offgets()and good test to prevent hacker exploit of entering a null character as the first character.
– chux
Nov 25 '18 at 20:52
Nice one.fgetsis of course preferable, but I added an answer on how to do withscanf
– Broman
Nov 25 '18 at 22:36
add a comment |
Good use offgets()and good test to prevent hacker exploit of entering a null character as the first character.
– chux
Nov 25 '18 at 20:52
Nice one.fgetsis of course preferable, but I added an answer on how to do withscanf
– Broman
Nov 25 '18 at 22:36
Good use of
fgets() and good test to prevent hacker exploit of entering a null character as the first character.– chux
Nov 25 '18 at 20:52
Good use of
fgets() and good test to prevent hacker exploit of entering a null character as the first character.– chux
Nov 25 '18 at 20:52
Nice one.
fgets is of course preferable, but I added an answer on how to do with scanf– Broman
Nov 25 '18 at 22:36
Nice one.
fgets is of course preferable, but I added an answer on how to do with scanf– Broman
Nov 25 '18 at 22:36
add a comment |
1
Swordfish has already given a good answer, and fgets is preferable to scanf. However, I want to show how you would use scanf in this case:
if(scanf("%599[^n]", input1) != 1) {
// Handle error
}
So what is different?
scanfreturns the number of successfully assignments, so if this returns 1, theninput1has been assigned. If not, an error has occured.- Changed
sto[^n]to read until newline - Inserted
599(one less than 600) so ensure that we don't write outside the array. - Removed
&frominput1. In this case, it would probably work anyway, but it is undefined behavior, which should be avoided at all costs.
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
add a comment |
1
Swordfish has already given a good answer, and fgets is preferable to scanf. However, I want to show how you would use scanf in this case:
if(scanf("%599[^n]", input1) != 1) {
// Handle error
}
So what is different?
scanfreturns the number of successfully assignments, so if this returns 1, theninput1has been assigned. If not, an error has occured.- Changed
sto[^n]to read until newline - Inserted
599(one less than 600) so ensure that we don't write outside the array. - Removed
&frominput1. In this case, it would probably work anyway, but it is undefined behavior, which should be avoided at all costs.
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
add a comment |
1
1
1
Swordfish has already given a good answer, and fgets is preferable to scanf. However, I want to show how you would use scanf in this case:
if(scanf("%599[^n]", input1) != 1) {
// Handle error
}
So what is different?
scanfreturns the number of successfully assignments, so if this returns 1, theninput1has been assigned. If not, an error has occured.- Changed
sto[^n]to read until newline - Inserted
599(one less than 600) so ensure that we don't write outside the array. - Removed
&frominput1. In this case, it would probably work anyway, but it is undefined behavior, which should be avoided at all costs.
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
Swordfish has already given a good answer, and fgets is preferable to scanf. However, I want to show how you would use scanf in this case:
if(scanf("%599[^n]", input1) != 1) {
// Handle error
}
So what is different?
scanfreturns the number of successfully assignments, so if this returns 1, theninput1has been assigned. If not, an error has occured.- Changed
sto[^n]to read until newline - Inserted
599(one less than 600) so ensure that we don't write outside the array. - Removed
&frominput1. In this case, it would probably work anyway, but it is undefined behavior, which should be avoided at all costs.
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
edited Nov 25 '18 at 23:09
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
answered Nov 25 '18 at 22:14
BromanBroman
7,249112644
7,249112644
add a comment |
add a comment |
-2
Try change your scanf line from:
scanf("%s", &input1);
to:
scanf("%[^n]", input1);
It worked out for me.
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
add a comment |
-2
Try change your scanf line from:
scanf("%s", &input1);
to:
scanf("%[^n]", input1);
It worked out for me.
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
add a comment |
-2
-2
-2
Try change your scanf line from:
scanf("%s", &input1);
to:
scanf("%[^n]", input1);
It worked out for me.
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
Try change your scanf line from:
scanf("%s", &input1);
to:
scanf("%[^n]", input1);
It worked out for me.
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
edited Nov 25 '18 at 23:03
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
answered Nov 25 '18 at 17:57
Anderson OliveiraAnderson Oliveira
876
876
add a comment |
add a comment |
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use
fgetsto read a line that contains spaces.strcspncan be used to remove the trailing newline.– xing
Nov 25 '18 at 17:41
3
In a situation like this, you should print the string that you have read to see what it contains. That's basic debugging.
– Broman
Nov 25 '18 at 17:42
1
scanffamously (yes; it is by design) separates input on spaces.– usr2564301
Nov 25 '18 at 17:43
5
"Standard library function X does not behave according to its documentation" is almost always a misdiagnosis. It is far more likely that the inputs are not what you think they are (as here), or even that you've misunderstood the docs.
– John Bollinger
Nov 25 '18 at 17:46
1
ericlippert.com/2014/03/05/how-to-debug-small-programs
– Broman
Nov 25 '18 at 17:51