数组

#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    double nums[15][15],sum=0,count=0;
    char c;
    cin >> c;
    for (int i = 0; i < 12; i++){
        for(int j =0;j < 12;j++){
            cin >> nums[i][j];
        }
    }
    int x =1;
    for (int i = 0;i < 11;i++){
        for (int j = x; j < 12; j++){
            sum += nums[i][j];
            count ++;
        }
        x++;
    }
    printf("%.1lf",c == 'S'? sum:sum/count);
    return 0;
}

不用数组

int main()
{
    double a,sum = 0;
    char c;
    cin >> c;
    int count = 0;
    for(int i = 0;i < 12;i++){
        for(int j = 0;j < 12;j++){
            cin >> a;
            if(j-i>=1) {
                sum += a;
                count ++;
            }
        }
    }
    printf("%.1lf",c == 'S'? sum:sum/count);
    return 0;
}