C Tutorial Int vs floating arithmatic
Introduction to C language
Integer types
Char constants
Int constants
Type combination and promotion
Int overflow
Floating point types
Assignment operator
Int vs float arithmatic
Mathematical operators
Unary Increment Operators
Pre and Post Variations
C Programming Cleverness and Ego Issues
Relational Operators
Logical Operators
Bitwise Operators
Other Assignment Operators





Here's an example of the sort of code where int vs. float arithmetic can cause problems. Suppose the following code is supposed to scale a homework score in the range 0..20 to be in the range 0..100.



int score;

...// suppose score gets set in the range 0..20 somehow

score = (score / 20) * 100;         // NO -- score/20 truncates to 0



Unfortunately, score will almost always be set to 0 for this code because the integer division in the expression (score/20) will be 0 for every value of score less than 20. The fix is to force the quotient to be computed as a floating point number...

score = ((double)score / 20) * 100; // OK -- floating point division from cast score = (score / 20.0) * 100; // OK -- floating point division from 20.0

score = (int)(score / 20.0) * 100;   // NO -- the (int) truncates the floating

// quotient back to 0

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