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cincrementoperator-precedencepost-incrementpre-increment

Output of multiple post and pre increments in one statement

I'm new to C language so please sum1 help me out. A C code written

int i=3;
printf("%d",++i + ++i);

Complier gives O/P =9. How?

Solution

  • The results are undefined. You're modifying a variable more than once in an expression (or sequence point to be more accurate).

    Modifying a variable more than once between sequence points is undefined, so don't do it.

    It might be your compiler, for this particular case decides to evalate ++i + ++i as

    • increment the last ++i , yielding 4, leaving i to be 4
    • increment the first ++i, yielding 5, leaving i to be 5 (as the prior step left i as 4, incrementing it to 5)
    • sum the two values, 4 + 5.

    Another compiler, or if you alter the optimization level, or if you change the code slightly, might produce different output.