Difference between revisions of "CSC231 Mystery C Program with signed numbers"
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| − | For reference, 2<sup>15</sup> = 32768. | + | For reference, 2<sup>15</sup> = 32768, and 2<sup>16</sup> = 65536. |
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=Solution= | =Solution= | ||
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;Answer 1 | ;Answer 1 | ||
* First we need to find the unsigned version of -32756, because that is the value we expected, but this value is too large to be represented in 2's complement. | * First we need to find the unsigned version of -32756, because that is the value we expected, but this value is too large to be represented in 2's complement. | ||
| − | * The difference between a negative 16-bit number in 2's complement, and its unsigned equivalent is 2<sup>16</sup>, | + | * The difference between a negative 16-bit number in 2's complement, and its unsigned equivalent is 2<sup>16</sup>, or 65536. |
* So, -32756 which is printed, has an unsigned value of -32756 + 65536 = 32780. | * So, -32756 which is printed, has an unsigned value of -32756 + 65536 = 32780. | ||
* So, x+y is 32740 and x+y+y = 32780 | * So, x+y is 32740 and x+y+y = 32780 | ||
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* [[CSC231_Mystery_C_Program_Solution | Solution Program]] | * [[CSC231_Mystery_C_Program_Solution | Solution Program]] | ||
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Latest revision as of 08:42, 4 November 2015
Mystery Program
- The program below is incomplete.
- The two values that were used to initialize x and y have been removed.
- We do have the output of the program, though, corresponding to the original x and y values.
- Question 1
- Figure out the value of x and y in the original program.
- Question 2
- Find a way to fix the program so that it outputs the correct information
You may use this converter to help you out...
/* mystery.cpp
// D. T.
// mystery program
// To compile and run this program:
//
// g++ mystery.cpp
// a.out
//
// The output of the program is the following
//
// 32740
// -32756
//
// With what positive values were x and y initialized
// at the beginning of the program. Explain why.
// (a short int contains 16 bits)
*/
#include <stdio.h>
int main() {
short int x = ???? ;
short int y = ???? ;
x = x+y;
printf( "%d\n", x );
x = x+y;
printf( "%d\n", x );
return 0;
}
For reference, 215 = 32768, and 216 = 65536.
