What is *山代码（能运行）

#include <bits/stdc++.h>
using namespace std;

int a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z;

int main() {
string a1;
getline(cin, a1); // 读入整行字符串

int len = a1.size();
for(int idx = 0; idx < len; idx++) {  // 循环变量不要用 i，和全局的 i 冲突
    if(a1[idx] == 'a' || a1[idx] == 'A')
        a++;
    else if(a1[idx] == 'b' || a1[idx] == 'B')
        b++;
    else if(a1[idx] == 'c' || a1[idx] == 'C')
        c++;
    else if(a1[idx] == 'd' || a1[idx] == 'D')
        d++;
    else if(a1[idx] == 'e' || a1[idx] == 'E')
        e++;
    else if(a1[idx] == 'f' || a1[idx] == 'F')
        f++;
    else if(a1[idx] == 'g' || a1[idx] == 'G')
        g++;
    else if(a1[idx] == 'h' || a1[idx] == 'H')
        h++;
    else if(a1[idx] == 'i' || a1[idx] == 'I')
        i++;
    else if(a1[idx] == 'j' || a1[idx] == 'J')
        j++;
    else if(a1[idx] == 'k' || a1[idx] == 'K')
        k++;
    else if(a1[idx] == 'l' || a1[idx] == 'L')
        l++;
    else if(a1[idx] == 'm' || a1[idx] == 'M')
        m++;
    else if(a1[idx] == 'n' || a1[idx] == 'N')
        n++;
    else if(a1[idx] == 'o' || a1[idx] == 'O')
        o++;
    else if(a1[idx] == 'p' || a1[idx] == 'P')
        p++;
    else if(a1[idx] == 'q' || a1[idx] == 'Q')
        q++;
    else if(a1[idx] == 'r' || a1[idx] == 'R')
        r++;
    else if(a1[idx] == 's' || a1[idx] == 'S')
        s++;
    else if(a1[idx] == 't' || a1[idx] == 'T')
        t++;
    else if(a1[idx] == 'u' || a1[idx] == 'U')
        u++;
    else if(a1[idx] == 'v' || a1[idx] == 'V')
        v++;
    else if(a1[idx] == 'w' || a1[idx] == 'W')
        w++;
    else if(a1[idx] == 'x' || a1[idx] == 'X')
        x++;
    else if(a1[idx] == 'y' || a1[idx] == 'Y')
        y++;
    else if(a1[idx] == 'z' || a1[idx] == 'Z')
        z++;
}

if(a > 0) cout << "a:" << a << endl;
if(b > 0) cout << "b:" << b << endl;
if(c > 0) cout << "c:" << c << endl;
if(d > 0) cout << "d:" << d << endl;
if(e > 0) cout << "e:" << e << endl;
if(f > 0) cout << "f:" << f << endl;
if(g > 0) cout << "g:" << g << endl;
if(h > 0) cout << "h:" << h << endl;
if(i > 0) cout << "i:" << i << endl;
if(j > 0) cout << "j:" << j << endl;
if(k > 0) cout << "k:" << k << endl;
if(l > 0) cout << "l:" << l << endl;
if(m > 0) cout << "m:" << m << endl;
if(n > 0) cout << "n:" << n << endl;
if(o > 0) cout << "o:" << o << endl;
if(p > 0) cout << "p:" << p << endl;
if(q > 0) cout << "q:" << q << endl;
if(r > 0) cout << "r:" << r << endl;
if(s > 0) cout << "s:" << s << endl;
if(t > 0) cout << "t:" << t << endl;
if(u > 0) cout << "u:" << u << endl;
if(v > 0) cout << "v:" << v << endl;
if(w > 0) cout << "w:" << w << endl;
if(x > 0) cout << "x:" << x << endl;
if(y > 0) cout << "y:" << y << endl;
if(z > 0) cout << "z:" << z << endl;

return 0;

}