程序代码：

#include<stdio.h>
#define R 26
char base[30]="ZABCDEFGHIJKLMNOPQRSTUVWXYZ";
void fun(int N)
{
    int i=0,j; char str[10];
    while(N>R)
    {
        str[i++]=base[N%R];
        N=N%R==0?N/R-1:N/R;
    }
    str[i]=base[N];
    for(j=i;j>=0;j--)
        printf("%c",str[j]);
    printf("\n");
}
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
        fun(n);
    return 0;
}

程序代码：

#include <stdio.h>

int main(void)
{
    unsigned n;
    int      tmp;
   
    scanf("%u", &n);    /* 输入0就会有意外出现，不过不应该输入0，可以在这里加一条if。*/
    tmp = n % 26;
    while (n != 26 && n / 26) {
        putchar('A');
        n /= 26;
    }
    putchar((tmp == 0 ? 25 : tmp - 1) + 'A');
   
    return 0;
}

程序代码：

1:  A
2:  B
3:  C
4:  D
5:  E
6:  F
7:  G
8:  H
9:  I
10: J
11: K
12: L
13: M
14: N
15: O
16: P
17: Q
18: R
19: S
20: T
21: U
22: V
23: W
24: X
25: Y
26: Z
27: AA
28: AB
29: AC
30: AD
31: AE
32: AF
33: AG
34: AH
35: AI
36: AJ
37: AK
38: AL
39: AM
40: AN
41: AO
42: AP
43: AQ
44: AR
45: AS
46: AT
47: AU
48: AV
49: AW
50: AX
51: AY
52: AZ