Why does this code produce 1 on adding characters in C?
-1
I was trying to restrict user input from alphabets (Eg: repeat input until correct input is provided ) , in order to get only numbers to be added. Somehow, instead of able to do so, I was able to add alphabets, but with out being '1'
It increments 1 if a number with a character is given.
#include<stdio.h>
int main() {
int x,y;
while(1)
{
printf("Enter a number > ");
if(scanf("%d%d",&x,&y) != 1){
printf("%d",x+y);
break;
}
}
return 0;
}
What could be the reason behind it?
c
edited Nov 13 '18 at 14:33
Loufi
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
add a comment |
-1
I was trying to restrict user input from alphabets (Eg: repeat input until correct input is provided ) , in order to get only numbers to be added. Somehow, instead of able to do so, I was able to add alphabets, but with out being '1'
It increments 1 if a number with a character is given.
#include<stdio.h>
int main() {
int x,y;
while(1)
{
printf("Enter a number > ");
if(scanf("%d%d",&x,&y) != 1){
printf("%d",x+y);
break;
}
}
return 0;
}
What could be the reason behind it?
c
edited Nov 13 '18 at 14:33
Loufi
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
2
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
1
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37
add a comment |
-1
-1
-1
I was trying to restrict user input from alphabets (Eg: repeat input until correct input is provided ) , in order to get only numbers to be added. Somehow, instead of able to do so, I was able to add alphabets, but with out being '1'
It increments 1 if a number with a character is given.
#include<stdio.h>
int main() {
int x,y;
while(1)
{
printf("Enter a number > ");
if(scanf("%d%d",&x,&y) != 1){
printf("%d",x+y);
break;
}
}
return 0;
}
What could be the reason behind it?
c
edited Nov 13 '18 at 14:33
Loufi
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
I was trying to restrict user input from alphabets (Eg: repeat input until correct input is provided ) , in order to get only numbers to be added. Somehow, instead of able to do so, I was able to add alphabets, but with out being '1'
It increments 1 if a number with a character is given.
#include<stdio.h>
int main() {
int x,y;
while(1)
{
printf("Enter a number > ");
if(scanf("%d%d",&x,&y) != 1){
printf("%d",x+y);
break;
}
}
return 0;
}
What could be the reason behind it?
c
c
edited Nov 13 '18 at 14:33
Loufi
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
edited Nov 13 '18 at 14:33
Loufi
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
edited Nov 13 '18 at 14:33
Loufi
15013
edited Nov 13 '18 at 14:33
Loufi
15013
edited Nov 13 '18 at 14:33
Loufi
15013
15013
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
asked Nov 13 '18 at 14:28
Sparsh_MishraSparsh_Mishra
67
67
2
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
1
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37
add a comment |
2
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
1
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37
2
2
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
1
1
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37
add a comment |
1 Answer
1
active
oldest
votes
1
scanf() returns the number of successful conversions it has performed for the input given.
With
scanf("%d%d", &x, &y)
you ask for two integers so scanf() will return 2 if it was successful. Your code however checks for != 1 which will also be true if scanf() returns 0 becuause you entered "a b" and no conversation could be performed.
If not all conversions were successful, all characters not being part of a successful conversion remain in stdin and the next scanf() will try to interpret them again and fail. To prevent that from happening you have to "clear" them:
#include <stdio.h>
int main()
{
while(1)
{
printf("Enter two numbers: ");
int x, y; // define variables as close to where they're used as possible
if (scanf("%d%d", &x, &y) == 2) {
printf("%dn", x + y);
break;
}
else {
int ch; // discard all characters until EOF or a newline:
while ((ch = getchar()) != EOF && ch != 'n');
}
}
return 0;
}
The more ideomatic way:
int x, y;
while (printf("Enter two numbers: "),
scanf("%d%d", &x, &y) != 2)
{
fputs("Input error :(nn", stderr);
int ch;
while ((ch = getchar()) != EOF && ch != 'n');
}
printf("%dn", x + y);
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
I think the check was for!= 1....so I guess OP knows this.
– Sourav Ghosh
Nov 13 '18 at 14:36
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you entera byour code will executeprintf("%dn", x + y);using garbage values forxandysince they were never written to and contain indeterminate values. For12 athe condition of yourifwon't be true and the nextscanf()will also fail returnin0your condition getting true andprintf("%dn", x + y);printing garbage.
– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
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active
oldest
votes
1
scanf() returns the number of successful conversions it has performed for the input given.
With
scanf("%d%d", &x, &y)
you ask for two integers so scanf() will return 2 if it was successful. Your code however checks for != 1 which will also be true if scanf() returns 0 becuause you entered "a b" and no conversation could be performed.
If not all conversions were successful, all characters not being part of a successful conversion remain in stdin and the next scanf() will try to interpret them again and fail. To prevent that from happening you have to "clear" them:
#include <stdio.h>
int main()
{
while(1)
{
printf("Enter two numbers: ");
int x, y; // define variables as close to where they're used as possible
if (scanf("%d%d", &x, &y) == 2) {
printf("%dn", x + y);
break;
}
else {
int ch; // discard all characters until EOF or a newline:
while ((ch = getchar()) != EOF && ch != 'n');
}
}
return 0;
}
The more ideomatic way:
int x, y;
while (printf("Enter two numbers: "),
scanf("%d%d", &x, &y) != 2)
{
fputs("Input error :(nn", stderr);
int ch;
while ((ch = getchar()) != EOF && ch != 'n');
}
printf("%dn", x + y);
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
I think the check was for!= 1....so I guess OP knows this.
– Sourav Ghosh
Nov 13 '18 at 14:36
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you entera byour code will executeprintf("%dn", x + y);using garbage values forxandysince they were never written to and contain indeterminate values. For12 athe condition of yourifwon't be true and the nextscanf()will also fail returnin0your condition getting true andprintf("%dn", x + y);printing garbage.
– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
add a comment |
1
scanf() returns the number of successful conversions it has performed for the input given.
With
scanf("%d%d", &x, &y)
you ask for two integers so scanf() will return 2 if it was successful. Your code however checks for != 1 which will also be true if scanf() returns 0 becuause you entered "a b" and no conversation could be performed.
If not all conversions were successful, all characters not being part of a successful conversion remain in stdin and the next scanf() will try to interpret them again and fail. To prevent that from happening you have to "clear" them:
#include <stdio.h>
int main()
{
while(1)
{
printf("Enter two numbers: ");
int x, y; // define variables as close to where they're used as possible
if (scanf("%d%d", &x, &y) == 2) {
printf("%dn", x + y);
break;
}
else {
int ch; // discard all characters until EOF or a newline:
while ((ch = getchar()) != EOF && ch != 'n');
}
}
return 0;
}
The more ideomatic way:
int x, y;
while (printf("Enter two numbers: "),
scanf("%d%d", &x, &y) != 2)
{
fputs("Input error :(nn", stderr);
int ch;
while ((ch = getchar()) != EOF && ch != 'n');
}
printf("%dn", x + y);
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
I think the check was for!= 1....so I guess OP knows this.
– Sourav Ghosh
Nov 13 '18 at 14:36
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you entera byour code will executeprintf("%dn", x + y);using garbage values forxandysince they were never written to and contain indeterminate values. For12 athe condition of yourifwon't be true and the nextscanf()will also fail returnin0your condition getting true andprintf("%dn", x + y);printing garbage.
– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
add a comment |
1
1
1
scanf() returns the number of successful conversions it has performed for the input given.
With
scanf("%d%d", &x, &y)
you ask for two integers so scanf() will return 2 if it was successful. Your code however checks for != 1 which will also be true if scanf() returns 0 becuause you entered "a b" and no conversation could be performed.
If not all conversions were successful, all characters not being part of a successful conversion remain in stdin and the next scanf() will try to interpret them again and fail. To prevent that from happening you have to "clear" them:
#include <stdio.h>
int main()
{
while(1)
{
printf("Enter two numbers: ");
int x, y; // define variables as close to where they're used as possible
if (scanf("%d%d", &x, &y) == 2) {
printf("%dn", x + y);
break;
}
else {
int ch; // discard all characters until EOF or a newline:
while ((ch = getchar()) != EOF && ch != 'n');
}
}
return 0;
}
The more ideomatic way:
int x, y;
while (printf("Enter two numbers: "),
scanf("%d%d", &x, &y) != 2)
{
fputs("Input error :(nn", stderr);
int ch;
while ((ch = getchar()) != EOF && ch != 'n');
}
printf("%dn", x + y);
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
scanf() returns the number of successful conversions it has performed for the input given.
With
scanf("%d%d", &x, &y)
you ask for two integers so scanf() will return 2 if it was successful. Your code however checks for != 1 which will also be true if scanf() returns 0 becuause you entered "a b" and no conversation could be performed.
If not all conversions were successful, all characters not being part of a successful conversion remain in stdin and the next scanf() will try to interpret them again and fail. To prevent that from happening you have to "clear" them:
#include <stdio.h>
int main()
{
while(1)
{
printf("Enter two numbers: ");
int x, y; // define variables as close to where they're used as possible
if (scanf("%d%d", &x, &y) == 2) {
printf("%dn", x + y);
break;
}
else {
int ch; // discard all characters until EOF or a newline:
while ((ch = getchar()) != EOF && ch != 'n');
}
}
return 0;
}
The more ideomatic way:
int x, y;
while (printf("Enter two numbers: "),
scanf("%d%d", &x, &y) != 2)
{
fputs("Input error :(nn", stderr);
int ch;
while ((ch = getchar()) != EOF && ch != 'n');
}
printf("%dn", x + y);
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
edited Nov 13 '18 at 14:56
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
answered Nov 13 '18 at 14:31
SwordfishSwordfish
9,06811335
9,06811335
I think the check was for!= 1....so I guess OP knows this.
– Sourav Ghosh
Nov 13 '18 at 14:36
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you entera byour code will executeprintf("%dn", x + y);using garbage values forxandysince they were never written to and contain indeterminate values. For12 athe condition of yourifwon't be true and the nextscanf()will also fail returnin0your condition getting true andprintf("%dn", x + y);printing garbage.
– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
add a comment |
I think the check was for!= 1....so I guess OP knows this.
– Sourav Ghosh
Nov 13 '18 at 14:36
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you entera byour code will executeprintf("%dn", x + y);using garbage values forxandysince they were never written to and contain indeterminate values. For12 athe condition of yourifwon't be true and the nextscanf()will also fail returnin0your condition getting true andprintf("%dn", x + y);printing garbage.
– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
I think the check was for
!= 1....so I guess OP knows this.– Sourav Ghosh
Nov 13 '18 at 14:36
I think the check was for
!= 1....so I guess OP knows this.– Sourav Ghosh
Nov 13 '18 at 14:36
1
1
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
The problem may be elsewhere....for a non-numeric input it'll keep failing as the input is not consumed, and would likely cause problem.
– Sourav Ghosh
Nov 13 '18 at 14:37
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
thanks for that one, but I'd like to learn more about the output produced, example: a+b results in 1 and 12+a results in 13
– Sparsh_Mishra
Nov 13 '18 at 14:39
If you enter
a b your code will execute printf("%dn", x + y); using garbage values for x and y since they were never written to and contain indeterminate values. For 12 a the condition of your if won't be true and the next scanf() will also fail returnin 0 your condition getting true and printf("%dn", x + y); printing garbage.– Swordfish
Nov 13 '18 at 14:42
If you enter
a b your code will execute printf("%dn", x + y); using garbage values for x and y since they were never written to and contain indeterminate values. For 12 a the condition of your if won't be true and the next scanf() will also fail returnin 0 your condition getting true and printf("%dn", x + y); printing garbage.– Swordfish
Nov 13 '18 at 14:42
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
@Swordfish 1) I never said the code was correct, it was referring to the then state of your answer, 2)the comment was made just before your expansion. :)
– Sourav Ghosh
Nov 13 '18 at 14:51
add a comment |
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2
Sorry...what? Can you make it more clear?
– Sourav Ghosh
Nov 13 '18 at 14:30
What input are you using exactly, what output are you getting, and what output did you expect?
– interjay
Nov 13 '18 at 14:31
1
restrict user input? dont use scanf then. use fgets/sscanf
– Anders
Nov 13 '18 at 14:33
@SouravGhosh I am using number as inputs, and trying to restrict the input to numbers. Basically trying to repeat the input process until i get 2 numbers. In case i give a character as input, the result is incremented by one (example input: a b) output : 1
– Sparsh_Mishra
Nov 13 '18 at 14:34
@interjay i used inputs : a b, i expected me to ask again for input, but the output produced was 1
– Sparsh_Mishra
Nov 13 '18 at 14:37