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- Steve Jobs

C Subtraction Without Using Minus Operator

subtraction without using minus operator

In my college days my programming friend makes a rigorous challenge with me. He asked me to subtract two numbers without using minus operator, it's sounds poor right. Subtraction without using minus operator is it possible for you?

You being a programmer, Impossible is nothing more than having two cups of coffee instead of a coffee, lets code a C program to subtract two numbers without using minus operator.

C Program - Without Using Subtraction Operator

c-without-subtraction-operator.c
#include <stdio.h>
int subtract(int, int);
int main()
{
int num1, num2;
printf("\nEnter any two integers : ");
scanf("%d%d", &num1, &num2);
printf("Result is %d ", subtract(num1, num2));
return 0;
}
int subtract(int num1, int num2)
{
int borrow;
while (num2 != 0)
{
borrow = (~num1) & num2;
num1 = num1 ^ num2;
num2 = borrow << 1;
}
return num1;
}
Enter any two integers : 6 4 
Result is : 2

Note:

The above program is crystal clear, we used function to subtract two numbers without using minus operator. We got two numbers from our user in a variable num1 and num2. Firstly, we check whether num2 is 0. If it's zero, just return a value in num1. If it's a non-zero number, then execute the statement following else.

Let us consider num1 = 6 and num2 = 4

Lets look closely in while-loop

borrow = (~num1) & num2; (line 1)

  • borrow = (~6) & 4;
  • borrow = (1001) & 0100 (in binary representation)
  • borrow = 0

borrow =num1 ^ num2; (line 2)

  • num1 = 6 ^ 4;
  • num1 = 0110 ^ 0100 (in binary representation)
  • num1 = 0010
  • num1 = 2

borrow = num1 ^ num2; (line 3)

  • num2 = borrow << 1;
  • num2 = 0 << 1 (in binary representation)
  • num2 = 0

In the first iteration itself num2 becomes 0. Thus value stored in num1 i.e) 2 is outputted.

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