Re: Suggested method for returning a string from a C program?

DFS <nospam@dfs.com> writes:
[...]

edit:  my attempt passed 9 of 14 tests, but fails on large N because
it's not calculating sum(1..N) correctly. Line 10.  See anything?
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//identify the missing number in a set of otherwise consecutive integers
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
int i = 0, N = 0, temp = 0;
int64_t totN = 0, totInputs = 0;
scanf("%d", &N);                 //number of elements
for (i = 0; i < N-1; i++) {      //list of elements
scanf("%d", &temp);      //to temp var
totInputs += temp;       //running total
}
totN = (N * (N + 1)) / 2;        //sum of numbers 1 to N

Since N is of type int, (N * (N + 1)) / 2 is of type int.  If it exceeds
INT_MAX, it overflows (undefined behavior, likely wraparound).  The fact
that you're assigning the result to an int64_t object doesn't change how
the expression is evaluated.

Remember, in most contexts, each C expression (including each
subexpression) is evaluated without regard to the context in which it
appears.  It's similar to the way that `double x = 1 / 3;` sets x to
0.0.

printf("N          %lld\n",N);
printf("tot N      %lld\n",totN);
printf("tot inputs %lld\n",totInputs);
printf("%d\n", totN - totInputs);  //solution
return 0;
}
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sample output
N          50000
tot N      -897458648  FAIL  (should be 1250025000)
tot inputs 1250017374  GOOD
-2147476022            FAIL  (should be 7626)

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */