Write a C program to input any number from user and find total number of leading zeros of the given number. How to find total leading zeros of a given number (in binary representation) using bitwise operator in C programming. Logic to count total leading zeros of a given number using C programming.

**Example**

**Input**

Input any number: 22

**Output**

Output leading zeros: 27 (using 4 byte signed integer)

## Required knowledge

Bitwise operators, Data types, Variables and Expressions, Basic input/output, If else, For loop

## Logic to count leading zeros in a binary number

Leading zeros in a binary number is equal to zeros preceding the highest order set bit of the number.

Step by step descriptive logic to count leading zeros in a binary number.

- Input number from user. Store it in some variable say,
`num`. - Find total bits required to store an integer in memory say,
`INT_SIZE = sizeof(int) * 8`

.Must know - How to find size of a data type using sizeof() operator.

- Initialize a variable and set its MSB to 1, say
`msb = 1 << (INT_SIZE - 1);`

. - Initialize a variable to store leading zeros count, say
`count = 0;`

. - Run a loop from 0 to
`INT_SIZE`. The loop structure should look like`for(i=0; i<INT_SIZE; i++)`

. - Inside the loop, left shift
`num`,`i`times and check its MSB is set or not. If its MSB is set i.e.`if((num << i) & msb)`

then terminate the loop; otherwise increment`count`by 1.

## Program to count leading zeros in a binary number

```
/**
* C program to count leading zeros in a binary number using bitwise operator
*/
#include <stdio.h>
#define INT_SIZE sizeof(int) * 8
int main()
{
int num, count, msb, i;
/* Input number from user */
printf("Enter any number: ");
scanf("%d", &num);
// Equivalent to
// 10000000 00000000 00000000 00000000
msb = 1 << (INT_SIZE - 1);
count = 0;
/* Iterate over each bit */
for(i=0; i<INT_SIZE; i++)
{
/* If leading set bit is found */
if((num << i) & msb)
{
/* Terminate the loop */
break;
}
count++;
}
printf("Total number of leading zeros in %d is %d", num, count);
return 0;
}
```

Below is another short and effective approach to solve the program.

## Program to count leading zeros in a binary number using while loop

```
/**
* C program to count leading zeros in a binary number using bitwise operator
*/
#include <stdio.h>
#include <limits.h> // Used for INT_MAX
int main()
{
int num, count;
/* Input number from user */
printf("Enter any number: ");
scanf("%d", &num);
count = 0;
while(!(num & (~INT_MAX)))
{
count++;
num <<= 1;
}
printf("Total number of leading zeros = %d", count);
return 0;
}
```

`INT_MAX`

is a constant defined in `limits.h`

header file. It is used to get maximum range of integer.

The statement `num <<= 1;`

is a shorthand assignment operator equivalent to `num = num << 1;`

Output

Enter any number: 22 Total number of leading zeros in 22 is 27

**Important Note:** Different compilers may yield different output. Since, data types size is machine dependent.

Happy coding 😉

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