Error cannot convert 'float*' to 'float' in return

Question

I'm new in C++ and I'm trying to learn about the arrays' behavior in functions. It's an attempt of matrix-vector multiplication.

#include <stdio.h>

#define N 4
float Gi[N][N] = {{ 0.0,         0.0,         0.0,         1.0},
                  { 0.0,  2.57142857,  3.42857143,  1.28571429},
                  {-0.0,  3.42857143,  8.57142857,  1.71428571},
                  { 1.0,  1.28571429,  1.71428571,  0.14285714}};

void mult(
        float vec_I[N],
        float vec_V[N]){
    int acc;
    for(int i = 0; i<N; i++){
        acc = 0;
        for(int j = 0; j<N; j++){
            acc += Gi[i][j]*vec_I[j];
            }
        vec_V[i] = acc;
    }
}

float solver(){
    float out[N];

    float I[N] = {0.0, 0.0, 0.0, 10.0};
    float V[N] = {0.0, 0.0, 0.0, 0.0};

    mult(I, V);
    
    out[0] = V[0];
    out[1] = V[1];
    out[2] = V[2];
    out[3] = V[3];
    return out;
}

int main(){
    float outPrint[4];

    outPrint = solver();

    printf("| %d |\n", outPrint[0]);
    printf("| %d |\n", outPrint[1]);
    printf("| %d |\n", outPrint[2]);
    printf("| %d |\n", outPrint[3]);

    return 0;
}

When I try to compile, the compiler tells me "[Error] cannot convert 'float*' to 'float' in return", about the return of the solver function (line 34). I can't understand why.

Answer 1

Arrays are not first-class citizens. As such they are not returnable by value. You will have to make use of a struct wrapper as such:

struct matrix_t
{
  float data[16];
};