# C Exercises: Count the numbers without digit 7, from 1 to a given number

## C Programming Mathematics: Exercise-22 with Solution

Write a C program to count the numbers without the digit 7, from 1 to a given number.

Example 1:

Input: n = 10

Output: 9

Example 2:

Input: n = 687

Output: 555

**Pictorial Presentation:**

**Sample Solution:**

**C Code:**

```
#include <stdio.h>
#include <stdlib.h>
int count_nums_not_7(int num)
{
if (num < 7)
return num;
if (num >= 7 && num < 10)
return num-1;
int r = 1;
while (num/r > 9)
r = r*10;
int m = num/r;
if (m != 7)
return count_nums_not_7(m)*count_nums_not_7(r - 1) + count_nums_not_7(m) + count_nums_not_7(num%r);
else
return count_nums_not_7(m*r - 1);
}
int main(void)
{
int n = 10;
if (n>0)
printf("Count the numbers without digit 7, from 1 to %d : %d", n, count_nums_not_7(n));
n = 687;
if (n>0)
printf("\nCount the numbers without digit 7, from 1 to %d : %d", n, count_nums_not_7(n));
}
```

Sample Output:

Count the numbers without digit 7, from 1 to 10 : 9 Count the numbers without digit 7, from 1 to 687 : 555

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