❮ C Unions C Examples Printf Double ❯

C Exercise Example 83

C Language Classic 100 Examples

Title: Calculate the number of odd numbers that can be formed with digits 0-7.

Program Analysis:

This problem is essentially a permutation and combination problem. Let's denote the number as sun=a1a2a3a4a5a6a7a8, where a1-a8 represent the digits of the number. If the last digit of a number is odd, then the number is odd, regardless of the preceding digits. If the last digit is even, then the number is even.

a1-a8 can take any of the digits 0-7, with the first digit not being 0.

We start counting the number of odd numbers from one-digit numbers to eight-digit numbers:

1. When there is only one digit, which is the last digit, the number of odd numbers is 4.
1. When the number has two digits, the number of odd numbers is 4*7=28.
1. When the number has three digits, the number of odd numbers is: 487=224.
...
1. When the number has eight digits, the number of odd numbers is: 4888888*7 (from the last digit to the first digit).

Example

//  Created by www.tutorialpro.org on 15/11/9.
//  Copyright © 2015年 tutorialpro.org. All rights reserved.
//

#include<stdio.h>
int main(int agrc, char*agrv[])
{
    long sum = 4, s = 4;//sum's initial value is 4, indicating the number of odd numbers with only one digit is 4.
    int j;
    for (j = 2; j <= 8; j++)
    {    
        printf("%d-digit odd number count: %ld\n", j-1, s);
        if (j <= 2)
            s *= 7;
        else
            s *= 8;
        sum += s;    
    }
    printf("%d-digit odd number count: %ld\n", j-1, s);
    printf("Total count of odd numbers: %ld\n", sum);
    // system("pause");
    return 0;
}

The above example outputs the following results when run:

1-digit odd number count: 4
2-digit odd number count: 28
3-digit odd number count: 224
4-digit odd number count: 1792
5-digit odd number count: 14336
6-digit odd number count: 114688
7-digit odd number count: 917504
8-digit odd number count: 7340032
Total count of odd numbers: 8388608

C Language Classic 100 Examples

❮ C Unions C Examples Printf Double ❯