Code that reads matrices from data files, and then computes their product and then prints the resultant matrix to data file

Question

#define n 50

void matread(char *, double [][n], int *, int *);
void matprint(double [][n],int ,int, char);
int matmul(int, int,int,int,int *, int *, double [][n],double [n][n], double [][n]);
void matprintf(double [][n], int, int, char *);


int main(){

    int ra,rb,rc,ca,cb,cc,flag;
    double a[n][n],b[n][n],c[n][n];
    FILE *fp;

    fp=fopen("matA.dat","w");
    fprintf(fp,"%d %d\n%.2lf %.2lf %.2lf\n%.2lf %.2lf %.2lf\n",2,3,
        1.0, 0.0, 4.0, -2.0, 4.0, 1.0);
    fclose(fp);

    fp=fopen("matB.dat","w");
    fprintf(fp,"%d %d\n%.2lf %.2lf %.2lf %.2lf \n%.2lf %.2lf %.2lf %.2lf \n%.2lf %.2lf %.2lf %.2lf\n",3,4,2.0,0.0,5.0, 1.0,4.0,0.0,-6.0,1.0,5.0,1.0,2.0,1.0);
    fclose(fp);

    matread("matA.dat",a,&ra,&ca);
    matprint(a,ra,ca,'A');
    matread("matB.dat",b,&rb,&cb);
    matprint(b,rb,cb,'B');
    flag=matmul(ra,ca,rb,cb,&rc,&cc,a,b,c);
    if(flag==0){
        printf("\nMatrices A and B are incompatiable for marix multiplication");
    }

    else{
        matprint(c,rc,cc,'C');
        matprintf(c,rc,cc,"matC.dat"); \\PROBLEM OCCURS WHEN THIS IS EXECUTED

    }


return 0;
}

void matprintf(double c[][n], int row, int col, char *file){

    FILE *fp;
    int i,j;
    fp=fopen(file,"w");
    printf(fp,"%d %d\n", row, col);
    for(i=0;i<row;++i){
        for(j=0;j<col;++j){
            fprintf(fp,"%lf ", c[i][j]);
        }
        printf("\n");
    }


}

int matmul(int ra, int ca,int rb,int cb,int *row, int *col,
 double a[][n], double b[n][n], double c[][n]){

    int i,j,k;
    if(ca!=rb) return 0;
    else {
        *row=ra;
        *col=cb;
        for(i=0;i<*row;++i){
            for(j=0;j<*col;++j){
                c[i][j]=0;
                for(k=0; k<cb; k++)
                    c[i][j]+= (a[i][k])*(b[k][j]);
            }
        }


    }
    return 1;


}
void matread(char *file, double a[][n], int *row, int *col){
    FILE *fp;
    int p,q,i,j;
    fp=fopen(file,"r");
    assert(fp!=NULL);
    fscanf(fp,"%d %d", &p, &q);
    *row=p;
    *col=q;

    for(i=0; i<*row; ++i){
        for(j=0;j<*col; ++j){
            fscanf(fp,"%lf",&a[i][j]);
        }
    }

}

void matprint(double a[][n],int row,int col, char c){

        int i,j;
        printf("Matrix %c is\n",c);
        for(i=0; i<row; ++i){
        for(j=0;j<col; ++j){
            printf("%.1lf ", a[i][j]);
        }
        printf("\n");
    }
}

This code is supposed to first extract matrices A and B from their respective data files matA.dat and matB.dat. These data files contain matrix size in first line, and matrix entries subsequently.

This is done using matread();(working) Then we print both these matrices using matprint(); (working)

Then it is supposed to check if they are compatible for multiplication(only checks for AB).

if not compatible, matmul() returns 0, if compatible matmul() computes AB, stores in C and returns 1; (working)

also if compatible, we're supposed to now print the matrix C into the data file matC.dat

Now this is where I am lost.

The question explicitly wants me to use this: matprintf(c,rc,cc,"matC.dat"); and then define matprintf() myself.

So my problem is that, first of all matC.dat is non existent at this point of time in main(), so how am I supposed to pass it as a file? Am I supposed to pass it as a string?

please help me.

Currently with this code I get the error:

matrix product.c:53:9: warning: incompatible pointer types passing 'FILE *' (aka 'struct __sFILE *') to parameter of type 'const char *' [-Wincompatible-pointer-types] printf(fp,"%d %d\n", row, col); ^~ /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h:170:36: note: passing argument to parameter here int printf(const char * __restrict, ...) __printflike(1, 2); ^ 1 warning generated.

Answer 1

You are passing fp to printf; printf doesn't take a file argument, but fprintf (as you are aware) does.