C中二维数组中一行的平均值？

Question

I am having trouble making a program that uses a function call to find the average of the rows in a two dimensional array? I can't get it to work in a larger program. I made this program to try and figure out what I am doing wrong, but to no avail. Any outside help would be greatly appreciated! Here is the testing code:

#include <stdio.h>
double dAvg(double pt[][5],int rows);
int main(void){
    int i;
    //Initiallize array
    double array[3][5]={{3.0,5.0,2.0,1.0,0.0},{4.0,8.0,6.0,3.0,3.0},{7.0,6.0,2.0,3.0,5.0}};
    //Computes the average value per row of array
    for(i=0;i < 3;i++){
        printf("The average of row %d is %f",i,dAvg(array,3));
    }
    return 0;
}
double dAvg(double pt[][5],int rows){
    int r,c;
    double sum,avg;
    //Calculate sum first
    for (c=0,sum=0;c<5;c++){
        sum += pt[r][c];
    //Find average by dividing the sum by the number of numbers in a row
    avg=sum/5;
    return avg;
    }
}

When I run the program, it just says that the program has stopped working, on top of that, I don't feel confident that I will actually work once that first issue is solved. I am quite new to multi-dimensional arrays and especially so for passing them to functions. Thanks again for any help!

Answer 1

Most errors were present in your dAvg function:

Namely:

1. You should not pass the entire 2D array if you only need one row there
2. You should pass the length of the array instead of hardcoding it everywhere (good practice, not a bug)
3. Your r was kept uninitialised therefore your indexing was not working
4. You were returning the average in every iteration therefore instead of summing the values you added the first and then you returned before adding the others.

double dAvg(double array[], size_t length){
    size_t c;
    double sum = 0;

    // Calculate sum first
    for (c = 0; c < length; c++){
        sum += array[c];
    }

    // Find average by dividing the sum by the number of numbers in a row
    return sum / (double) length;
} 

int main(void){
    int i;
    //Initiallize array
    double array[3][5] = {{3.0,5.0,2.0,1.0,0.0}, {4.0,8.0,6.0,3.0,3.0}, {7.0,6.0,2.0,3.0,5.0}};

    //Computes the average value per row of array
    for(i = 0; i < 3; i++){
        printf("The average of row %d is %f\n", i, dAvg(array[i], 5));
    }

    return 0;
}