Subtraction without minus sign in C

Question

How can I subtract two integers in C without the - operator?

Answer 1

This would work using integer overflow:

#include<limits.h>    
int subtractWithoutMinusSign(int a, int b){
         return a + (b * (INT_MAX + INT_MAX + 1));
}

This also works for floats (assuming you make a float version…)

Answer 2

Not tested. Without using 2's complement:

#include <stdlib.h>
#include <stdio.h>
int sillyNegate(int x) {
   if (x <= 0)
     return abs(x);
   else {
     // setlocale(LC_ALL, "C"); // if necessary.
     char buffer[256];
     snprintf(buffer, 255, "%c%d", 0x2d, x);
     sscanf(buffer, "%d", &x);
     return x;
   }
}

Assuming the length of an int is much less than 255, and the snprintf/sscanf round-trip won't produce any unspecified behavior (right? right?).

The subtraction can be computed using a - b == a + (-b).

---

Alternative:

#include <math.h>
int moreSillyNegate(int x) {
   return x * ilogb(0.5);  // ilogb(0.5) == -1;
}

---

Answer 3

        int num1, num2, count = 0;
        Console.WriteLine("Enter two numebrs");
        num1 = int.Parse(Console.ReadLine());
        num2 = int.Parse(Console.ReadLine());
        if (num1 < num2)
        {
            num1 = num1 + num2;
            num2 = num1 - num2;
            num1 = num1 - num2;
        }
        for (; num2 < num1; num2++)
        {
            count++;
        }
        Console.WriteLine("The diferrence is " + count);

Answer 4

For the maximum range of any data type , one's complement provide the negative value decreased by 1 to any corresponding value. ex:
~1 --------> -2
~2---------> -3
and so on... I will show you this observation using little code snippet

#include<stdio.h>
int main()
{
   int a , b;
   a=10;
   b=~a; // b-----> -11    
   printf("%d\n",a+~b+1);// equivalent to a-b
   return 0;
}

Output: 0
Note : This is valid only for the range of data type. means for int data type this rule will be applicable only for the value of range[-2,147,483,648 to 2,147,483,647]. Thankyou .....May this help you

Answer 5

void main()
{
int a=5;
int b=7;

while(b--)a--;
printf("sud=%d",a);

}

Answer 6

• + No bit setting
• + Language independent
• + Can be adjusted for different number types (int, float, etc)
• - Almost certainly not your C homework answer (which is likely to be about bits)

Expand a-b:

a-b = a + (-b)
    = a + (-1).b

Manufacture -1:

float:             pi = asin(1.0);
(with    minusone_flt = sin(3.0/2.0*pi);
math.h)           or  = cos(pi)
                  or  = log10(0.1)
complex: minusone_cpx = (0,1)**2; // i squared
integer: minusone_int = 0; minusone_int--; // or convert one of the floats above