Can scanf () turn non-zero input to zero

Question

In the following code, scanf () in main () turns one of the input numbers from a nonzero number to zero, as shown by debugging printf () in a while loop. I tested it on several compilers, but only to get the same result. Please help me by telling me why this is so. Thank.

 #include <stdio.h>

unsigned srl (unsigned x, int k)
{
    /* perform shift arithmetically */
    printf("x = %u, (int) x= %d\n", x, (int) x);
    unsigned xsra = (int) x >> k;
    printf("\nxsra before was: %u\n", xsra);
    unsigned test = 0xffffffff;
    test <<= ((sizeof (int) << 3) - k); // get e.g., 0xfff00...
    printf("test after shift is: %x, xsra & test = %x\n", test, xsra & test);
    if (xsra & test == 0) // if xsrl is positve
        return xsra;
    else
        xsra ^= test;    // turn 1s into 0s

    return xsra;
}

int sra (int x, int k) 
{
    /* perform shift logically */
    int xsrl = (unsigned) x >> k;
    unsigned test = 0xffffffff;
    test << ((sizeof (int) << 3) - k + 1); // get e.g., 0xffff00...
    if (xsrl & test == 0) // if xsrl is positve
        return xsrl;
    else 
                            xsrl |= test;

        return xsrl;
}

int main(void)
{
    int a;
    unsigned b;
    unsigned short n;

    puts("Enter an integer and a positive integer (q or negative second number to quit): ");
    while(scanf("%d%u", &a, &b) == 2 && b > 0)
    {
        printf("Enter the number of shifts (between 0 and %d): ", (sizeof (int) << 3) - 1);
        scanf("%d", &n);
        if (n < 0 || n >= ((sizeof (int)) << 3))
        {
            printf("The number of shifts should be between 0 and %d.\n", ((sizeof (int)) << 3) - 1);
            break;
        }
        printf("\nBefore shifting, int a = %d, unsigned b = %u\n", a, b);
        a = sra(a, n);
        b = srl(b, n);
        printf("\nAfter shifting, int a = %d, unsigned b = %u\n", a, b);
        puts("\nEnter an integer and a positive integer (q or negative second number to quit): ");
    }
    puts("Done!");

    return 0;
}

Answer 1

The problem is what nis unsigned short, which is smaller than normal int. When you call scanf("%d", &n);, it reads the value in nand potentially overwrites the existing value bif it bhas a memory location immediately after n.

, , :

scanf("%hu", &n);

h unsigned short int, .