I put my efforts to write a c program for multiplication of rectangular matrices, but when compiled and run the program, the resultant matrix is not printed with the products. As user inputs, I tried entering 2 rows and 3 columns for the Matrix A, and 3 rows and 2 columns for the Matrix B.
How can I correct the below code?
#include<stdio.h>
int main()
{
int i,j,r,c,r1,c1,r2,c2,k,a[10][10],b[10][10],result[10][10];
printf("\n Enter the no. of rows and column desired for the 1st matrix (between 1 to 10):");
scanf("%d%d",&r1,&c1);
printf("\n Enter the no. of rows and columns for the 2nd matrix - between 1 to 10 (Pls note that no. of rows of 1st matrix should be equal to the no. of columns in the 2nd matrix for multiplication):");
scanf("%d%d",&r2,&c2);
printf("\n Enter the elements of the 1st Matrix:");
for(i=0;i<r1;i++){
for(j=0;j<c1;j++){
scanf("%d",&a[i][j]);
}
}
printf("\n Print of 1st Matrix:\n");
for(i=0;i<r1;i++){
for(j=0;j<c1;j++){
printf("\t%d",a[i][j]);
}
printf("\n");
}
printf("\n Enter the elements of the 2nd Matrix:");
for(i=0;i<r2;i++){
for(j=0;j<c2;j++){
scanf("%d",&b[i][j]);
}
}
printf("\n Print of 2nd Matrix:\n");
for(i=0;i<r2;i++){
for(j=0;j<c2;j++){
printf("\t%d",b[i][j]);
}
printf("\n");
}
//multiplying 1st and 2nd matrices and storing the results in results[i][j]
for(i=0;i<r1;i++){
for(j=0;j<c2;j++){
for(k=0;k<c1;k++){
result[i][j] = result[i][j] + (a[i][k] * b[k][j]);
}
}
}
//Printing the results
printf("\n After Multiplication of two matrices:\n");
for(i=0;i<r;i++){
for(j=0;j<c;j++){
printf("\t%d",result[i][j]);
}
printf("\n");
}
return 0;
}
In your code there are some problems.
Result matrix initialization
I suggest you to change the code in this way
//multiplying 1st and 2nd matrices and storing the results in results[i][j]
for(i=0;i<r1;i++){
for(j=0;j<c2;j++){
//init i,j element of result matrix
result[i][j] = 0; //add here the initialisation
for(k=0;k<c1;k++){
result[i][j] = result[i][j] + (a[i][k] * b[k][j]);
}
}
}
Cycle for printing output
In your code you used the variable r and c without initizialize them. this is the main cause of wrong output.
Change the code in this way:
for(i=0;i<r1;i++){
for(j=0;j<c2;j++){
printf("\t%d",result[i][j]);
}
printf("\n");
}
The new code
Here there is the completed code of your program with corrections and some improvements in scanf statements.
#include<stdio.h>
int main()
{
int i,j,r1,c1,r2,c2,k,a[10][10],b[10][10];
int result[10][10];
printf("\n Enter the no. of rows and column desired for the 1st matrix (between 1 to 10):");
scanf("%d %d",&r1,&c1); //put a space between escape codes in order to avoid conversion issues
printf("\n Enter the no. of rows and columns for the 2nd matrix - between 1 to 10 (Pls note that no. of rows of 1st matrix should be equal to the no. of columns in the 2nd matrix for multiplication):");
scanf("%d %d",&r2,&c2); //put a space between escape codes in order to avoid conversion issues
printf("\n Enter the elements of the 1st Matrix:");
for(i=0;i<r1;i++){
for(j=0;j<c1;j++){
scanf("%d",&a[i][j]);
}
}
printf("\n Print of 1st Matrix:\n");
for(i=0;i<r1;i++){
for(j=0;j<c1;j++){
printf("\t%d",a[i][j]);
}
printf("\n");
}
printf("\n Enter the elements of the 2nd Matrix:");
for(i=0;i<r2;i++){
for(j=0;j<c2;j++){
scanf("%d",&b[i][j]);
}
}
printf("\n Print of 2nd Matrix:\n");
for(i=0;i<r2;i++){
for(j=0;j<c2;j++){
printf("\t%d",b[i][j]);
}
printf("\n");
}
//multiplying 1st and 2nd matrices and storing the results in results[i][j]
for(i=0;i<r1;i++){
for(j=0;j<c2;j++){
//init i,j element of result matrix
result[i][j] = 0.0;
for(k=0;k<c1;k++){
printf("(%d %d %d) %f - %d - %d\n",i,j,k,result[i][j],a[i][k],b[k][j]);
result[i][j] = result[i][j] + (a[i][k] * b[k][j]);
}
}
}
//Printing the results
printf("\n After Multiplication of two matrices:\n");
for(i=0;i<r1;i++){
for(j=0;j<c2;j++){
printf("\t%d",result[i][j]);
}
printf("\n");
}
return 0;
}