Different output for different compiler - C and C++ [duplicate]

Answer 1

int main() { return sizeof 'a'; }

Answer 2

This program produces 12 in C++ or C99, and 6 in C89:

#include <stdio.h>

int main()
{
    int a = 12//**/2;
    ;

    printf("%d\n", a);
    return 0;
}

Answer 3

#include <stdio.h>
int main(void)
{
#ifdef __cplusplus
    puts("C++");
#else
    puts("C");
#endif
    return 0;
}

Answer 4

typedef char X;
int main() {
    struct X { double foo; }
    printf("%d\n", sizeof(X));
    return 0;
}

Answer 5

int class;

Will not compile in C++ and will compile in C.

Answer 6

From wikipedia, altered to produce consistent output in each language:

extern int T;

int size(void)
{
    struct T {  int i;  int j;  };

    return sizeof(T) == sizeof(int);
    /* C:   return 1
    *  C++: return 0
    */
}