Arduino: incorrect calculation of long integer
I'm doing a simple calculation with integers (on Arduino with ESP8266 12E), but I can't get the expected result and can't find the error. Can someone guide me?
#define A 200
#define B A * 62
#define C 500
void setup() {
Serial.begin(9600);
Serial.println("");
unsigned long aux = 0;
aux = (B * 500) / C; // (12400 * 500) / 500 = 12400
Serial.printf("aux = %dn", aux);
aux = aux * C; // 12400 * 500 = 6200000
Serial.printf("aux = %dn", aux);
// ERROR: Should result in "500", but is resulting in "1922000"
aux = aux / B; // 6200000 / 12400 = 500
Serial.printf("aux = %dn", aux); // It's printing "1922000"
}
esp8266
asked 2 hours ago
wBB
1133
migrated from electronics.stackexchange.com 17 mins ago
This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.
add a comment |
I'm doing a simple calculation with integers (on Arduino with ESP8266 12E), but I can't get the expected result and can't find the error. Can someone guide me?
#define A 200
#define B A * 62
#define C 500
void setup() {
Serial.begin(9600);
Serial.println("");
unsigned long aux = 0;
aux = (B * 500) / C; // (12400 * 500) / 500 = 12400
Serial.printf("aux = %dn", aux);
aux = aux * C; // 12400 * 500 = 6200000
Serial.printf("aux = %dn", aux);
// ERROR: Should result in "500", but is resulting in "1922000"
aux = aux / B; // 6200000 / 12400 = 500
Serial.printf("aux = %dn", aux); // It's printing "1922000"
}
esp8266
asked 2 hours ago
wBB
1133
migrated from electronics.stackexchange.com 17 mins ago
This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.
add a comment |
I'm doing a simple calculation with integers (on Arduino with ESP8266 12E), but I can't get the expected result and can't find the error. Can someone guide me?
#define A 200
#define B A * 62
#define C 500
void setup() {
Serial.begin(9600);
Serial.println("");
unsigned long aux = 0;
aux = (B * 500) / C; // (12400 * 500) / 500 = 12400
Serial.printf("aux = %dn", aux);
aux = aux * C; // 12400 * 500 = 6200000
Serial.printf("aux = %dn", aux);
// ERROR: Should result in "500", but is resulting in "1922000"
aux = aux / B; // 6200000 / 12400 = 500
Serial.printf("aux = %dn", aux); // It's printing "1922000"
}
esp8266
asked 2 hours ago
wBB
1133
I'm doing a simple calculation with integers (on Arduino with ESP8266 12E), but I can't get the expected result and can't find the error. Can someone guide me?
#define A 200
#define B A * 62
#define C 500
void setup() {
Serial.begin(9600);
Serial.println("");
unsigned long aux = 0;
aux = (B * 500) / C; // (12400 * 500) / 500 = 12400
Serial.printf("aux = %dn", aux);
aux = aux * C; // 12400 * 500 = 6200000
Serial.printf("aux = %dn", aux);
// ERROR: Should result in "500", but is resulting in "1922000"
aux = aux / B; // 6200000 / 12400 = 500
Serial.printf("aux = %dn", aux); // It's printing "1922000"
}
esp8266
esp8266
asked 2 hours ago
wBB
1133
asked 2 hours ago
wBB
1133
asked 2 hours ago
wBB
1133
asked 2 hours ago
wBB
1133
asked 2 hours ago
wBB
1133
1133
migrated from electronics.stackexchange.com 17 mins ago
This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.
migrated from electronics.stackexchange.com 17 mins ago
This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
In your #define of B you missed parenthesis (). Change your definition to:
#define B (A * 62)
Without parenthesis you first divide 6200000 by 200 and then multiply result by 62, which is not what you intend.
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
add a comment |
Fully-parenthesizing macros (as noted in answer by dmz) solves one class of problem.
Another thing you should do is, in any arithmetic expression which involves literal constants, use the L suffix on at least one of the constants involved if there's any chance the result will exceed 32767 (the maximum guaranteed-representable value for int). The type of an arithmetic operation in C is based on the types of the operands of that operation only; the type of the variable to which the result is assigned is irrelevant.
answered 35 mins ago
mlp
101
1
...and the format specifier for anunsigned longis%lunot%d- the compiler for the asker's esp8266 uses a 32-bitintso they get away with some things they would not on an ATmega-based Arduino where anintis the minimum 16 bit size allowed by the specification.
– Chris Stratton
32 mins ago
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
In your #define of B you missed parenthesis (). Change your definition to:
#define B (A * 62)
Without parenthesis you first divide 6200000 by 200 and then multiply result by 62, which is not what you intend.
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
add a comment |
In your #define of B you missed parenthesis (). Change your definition to:
#define B (A * 62)
Without parenthesis you first divide 6200000 by 200 and then multiply result by 62, which is not what you intend.
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
add a comment |
In your #define of B you missed parenthesis (). Change your definition to:
#define B (A * 62)
Without parenthesis you first divide 6200000 by 200 and then multiply result by 62, which is not what you intend.
In your #define of B you missed parenthesis (). Change your definition to:
#define B (A * 62)
Without parenthesis you first divide 6200000 by 200 and then multiply result by 62, which is not what you intend.
answered 2 hours ago
dmz
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
add a comment |
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
Dude, you're 100% right. I've spent several hours trying to figure out what was wrong ... Thank you so much!
– wBB
2 hours ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
@wBB remember that in C, macros are replaced in the code, exactly as you wrote them, in the preprocessor step before the code gets compiled. So it helps as a sanity-check in these cases to expand the macros yourself in your code to see if you're getting what you intended.
– brhans
1 hour ago
add a comment |
Fully-parenthesizing macros (as noted in answer by dmz) solves one class of problem.
Another thing you should do is, in any arithmetic expression which involves literal constants, use the L suffix on at least one of the constants involved if there's any chance the result will exceed 32767 (the maximum guaranteed-representable value for int). The type of an arithmetic operation in C is based on the types of the operands of that operation only; the type of the variable to which the result is assigned is irrelevant.
answered 35 mins ago
mlp
101
1
...and the format specifier for anunsigned longis%lunot%d- the compiler for the asker's esp8266 uses a 32-bitintso they get away with some things they would not on an ATmega-based Arduino where anintis the minimum 16 bit size allowed by the specification.
– Chris Stratton
32 mins ago
add a comment |
Fully-parenthesizing macros (as noted in answer by dmz) solves one class of problem.
Another thing you should do is, in any arithmetic expression which involves literal constants, use the L suffix on at least one of the constants involved if there's any chance the result will exceed 32767 (the maximum guaranteed-representable value for int). The type of an arithmetic operation in C is based on the types of the operands of that operation only; the type of the variable to which the result is assigned is irrelevant.
answered 35 mins ago
mlp
101
1
...and the format specifier for anunsigned longis%lunot%d- the compiler for the asker's esp8266 uses a 32-bitintso they get away with some things they would not on an ATmega-based Arduino where anintis the minimum 16 bit size allowed by the specification.
– Chris Stratton
32 mins ago
add a comment |
Fully-parenthesizing macros (as noted in answer by dmz) solves one class of problem.
Another thing you should do is, in any arithmetic expression which involves literal constants, use the L suffix on at least one of the constants involved if there's any chance the result will exceed 32767 (the maximum guaranteed-representable value for int). The type of an arithmetic operation in C is based on the types of the operands of that operation only; the type of the variable to which the result is assigned is irrelevant.
answered 35 mins ago
mlp
101
Fully-parenthesizing macros (as noted in answer by dmz) solves one class of problem.
Another thing you should do is, in any arithmetic expression which involves literal constants, use the L suffix on at least one of the constants involved if there's any chance the result will exceed 32767 (the maximum guaranteed-representable value for int). The type of an arithmetic operation in C is based on the types of the operands of that operation only; the type of the variable to which the result is assigned is irrelevant.
answered 35 mins ago
mlp
101
answered 35 mins ago
mlp
101
answered 35 mins ago
mlp
101
answered 35 mins ago
mlp
101
101
1
...and the format specifier for anunsigned longis%lunot%d- the compiler for the asker's esp8266 uses a 32-bitintso they get away with some things they would not on an ATmega-based Arduino where anintis the minimum 16 bit size allowed by the specification.
– Chris Stratton
32 mins ago
add a comment |
1
...and the format specifier for anunsigned longis%lunot%d- the compiler for the asker's esp8266 uses a 32-bitintso they get away with some things they would not on an ATmega-based Arduino where anintis the minimum 16 bit size allowed by the specification.
– Chris Stratton
32 mins ago
1
1
...and the format specifier for an
unsigned long is %lu not %d - the compiler for the asker's esp8266 uses a 32-bit int so they get away with some things they would not on an ATmega-based Arduino where an int is the minimum 16 bit size allowed by the specification.– Chris Stratton
32 mins ago
...and the format specifier for an
unsigned long is %lu not %d - the compiler for the asker's esp8266 uses a 32-bit int so they get away with some things they would not on an ATmega-based Arduino where an int is the minimum 16 bit size allowed by the specification.– Chris Stratton
32 mins ago
add a comment |
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