Arithmetic and the Integer-Division Trap
beginner11 min readLesson 11 of 148
The arithmetic operators, increment/decrement, and why 1/2 is 0 in C.
Arithmetic
+ - * / % — add, subtract, multiply, divide, remainder. % (modulo) is
integer-only and gives the remainder: 7 % 3 is 1.
The trap: int / int is int
printf("%d\n", 1 / 2); // 0 — integer division truncates
printf("%f\n", 1.0 / 2); // 0.500000 — one double promotes all
printf("%d\n", 7 % 3); // 1
When both operands are integers, / truncates toward zero. This single rule
explains a huge share of beginner bugs (averages that print 0, percentages
stuck at 100).
Increment and decrement
int i = 5;
i++; // i is 6 (post-increment: value of i++ is the OLD 5)
++i; // pre-increment: value is the NEW 6
Prefer standalone i++ statements; the difference between pre/post only
matters when the expression's value is used.