my code works fine, but want to replace the last for-loop in main, that checks the number of bits on in uint32 with some more optimised code?

basically i used uint32 to store the 26 alphabets. Parse each string and turn ON the corresponding bit in uint32 and return the variable. Which is bitwise-AND with master uint32 variable.

unsigned int processing (const std::string& str) {
// find out and return the number of 'chars' that 
unsigned int tmp = 0x00000000;
auto endpt = str.end()
for (auto iter = str.begin(); iter != endpt; iter++) {
    int val = 'z' - *iter;
    //cout << "cur val: " << *iter <<" : " << val << endl;
    tmp |= (0x00000001 << val);
}
return tmp;
}

int main() {
/* Enter your code here. Read input from STDIN. Print output to STDOUT */   
int t;
cin >> t;

char master_list[CNT];
unsigned int can = 0xEFFFFFFF;
for (int i=0; i < CNT; i++) master_list[i] = 'x';
int ret = 0;
while (t--) {
    std::string arr;
    cin >> arr;
    //cout << "input: "<< arr << endl;
    can &= processing(arr);
}
//cout << "result: " << hex << can << endl;
// finding number of bits ON in uint32
unsigned int a = 0x00000001;
int count = 0;
for (int i =0; i<32; i++) {
    if ((can & a) != 0) count++;
    a = a << 1;
}
cout << count << endl;
return 0;
}