维吉尼亚密码破解时输出有问题

维吉尼亚密码破解时求密钥mg移位时有一行全为nan：

代码如下：

#include<iostream>
#include<string>
using namespace std;

string* makeGroup(string beforeText, int step) {  
    string* afterText = new string[step];  
    long length = beforeText.length();  
    for (long i = 0; i < length; i++) {  
        afterText[i % step] += beforeText[i];  
    }  
    return afterText;  
}

//求密钥长度，根据不同密钥长度对应的重合指数，正常文本为0.0635左右
int GetKeyLength(string cipherText){
    //尝试1-30的密钥长度
    double smallest = 1;
    int keyLength = 0;
    for (int i = 1; i < 30; i++) {
        double index = 0;
        string* afterText = makeGroup(cipherText, i);
        for (int j = 0; j < i; j++) {
            double num = 0;
            //ASCII码65-90对应A-Z
            for (int p = 65; p < 91; p++) {
                int count = 0;
                for (int q = 0; q < afterText[j].length(); q++) {
                    if (afterText[j][q] == p) {
                        count++;
                    }
                }
                num += (double(count) / afterText[j].length()) * ((double(count) - 1) / (afterText[j].length() - 1));
            }
            index += num;
        }
        cout <<"密钥长度为"<<i<<"时，重合指数="<< index / i << endl;
    }
    return keyLength;
}

//寻找mg移位，确定密钥
void Getkey(string a,int keylength){
    double x[26]={0.082,0.015,0.028,0.043,0.127,0.022,0.020,0.061,0.070,0.002,0.008,0.040,0.024,0.067,0.075,0.019,0.001,0.060,0.063,0.091,0.028,0.010,0.023,0.001,0.020,0.001};
     string* afterText=makeGroup(a,keylength);
     for(int i=0;i<keylength;i++){
         int l=65;
         double count[keylength][26];
         for(int j=0;j<26;j++){
             l=65+j;
             for(int k=0;k<(a.length()/keylength);k++){
                 if(afterText[i][k]==l){
                     count[i][j]++;
                }
            }
        }
        for(int j=0;j<26;j++){
            double m=0;
            for(int t=0;t<26;t++){
                m+=x[t]*count[i][(t+j)%26]/(double)(a.length()/keylength);
            }
            cout<<m<<" ";
        }
        cout<<endl;
     }
} 

int main(){
    string a="KCCPKBGUFDPHQTYAVINRRTMVGRKDNBVFDETDGILTXRGUDDKOTFMBPVGEGLTGCKQRACQCWDNAWCRXIZAKFTLEWRPTYCQKYVXCHKFTPONCQQRHJVAJUWETMCMSPKQDYHJVDAHCTRLSVSKCGCZQQDZXGSFRLSWCWSJTBHAFSIASPRJAHKJRJUMVGKMITZHFPDISPZLVLGWTFPLKKEBDPGCEBSHCTJRWXBAFSPEZQNRWXCVYCGAONWDDKACKAWBBIKFTIOVKCGGHJVLNHIFFSQESVYCLACNVRWBBIREPBBVFEXOSCDYGZWPFDTKFQIYCWHJVLNHIQIBTKHJVNPIST";
    GetKeyLength(a);
    Getkey(a,6);
}

请解答！

估计是出现分母为0的情况了吧
我在VS2010下测试没问题，但有一个地方注意double count[keylength][26];没有初始化。后面都是count[i][j]++;有问题

Getkey()函数中count数组没有初始化，后面++计算的时候出错。
把 double count[keylength] [26] ; 改成 double count[100][26]={0}; 试一下。