只用加法與位移做出乘法

 #include <stdio.h>

unsigned int multiplier_fun(unsigned int mulcand, unsigned int mul)

{

    unsigned int max_num, i, total;

    if ((mulcand == 0) || (mul == 0))

        return 0;

    for (max_num = 31; max_num > 0; max_num--)

    {

        if (mul & (1 << max_num))

            break;

    }

    total = 0;

    for (i = 0; i <= max_num; i++)

    {

        if (mul & (1 << i))

        {

            total += (mulcand << i);

        }

    }

    return total;

}

int main()

{

    unsigned int var_a, var_b;

    printf("\nPlease input a and b values:");

    scanf("%d %d", &var_a, &var_b);

    printf("\n=============================================\n");

    printf("%d x %d = %d", var_a, var_b, multiplier_fun(var_a, var_b));

    printf("\n=============================================\n");

    return 0;

}

Please input a and b values:9 19 ============================================= 9 x 19 = 171 =============================================

Please input a and b values:3 133

=============================================

3 x 133 = 399

=============================================