Multiply a line of a matrix by a number given - c

Question

I'm supposed to multiply a certain line (I specify what line exactly in the 4th argument of the function) of a given matrix by a number.
The main function:
int main_tp05(int argc, const char *argv[]){
int mNx100[][MAXCOLS100] = {{1,2,3},{4,5,6},{7,8,9}};
multiply_matrixNx100_line_by_scalar(mNx100,3,3,1,2);
return 0;
}
I've tried to solve it like so:
void multiply_matrixNx100_line_by_scalar(int mNx100[][MAXCOLS100], int lines, int columns, int line, int scalar){
for (int i = 0; i < lines; i++) {
for (int j = 0; j < columns; j++) {
if(i == line){
printf("%d\n", mNx100[i*scalar][j] );
}
}
printf("\n");
}
}
To note that:
1- I can´t change the parameters.
2- MAXCOLS100 is a macro on the .h file. I put it with the value of 3.
3- The scalar is the number I want to multiply the line by.

Answer 1

I WROTE THIS CODING AND VERIFIED BY MYSELF IT WORKS SUCCESSFULLY.
#include <stdio.h>
#include <stdlib.h>
int main()
{
int i,j,a[5][5],b,c,d,m,n,r;
printf("Enter the number of rows and columns\n");
scanf("%d %d",&m,&n);
printf("Enter the matrix\n");
for(i=1;i<=m;i++)
{
for(j=1;j<=n;j++)
{
scanf("%d",&a[i][j]);
}
}
printf("Enter the number to multiply the matrix\n");
scanf("%d",&b);
printf("Enter 0 to multiply row or 1 to multiply column\n");
scanf("%d",&d);
if(d==0)
{
printf("Enter the row number to be multiplied\n");
scanf("%d",&r);
for(i=r,j=1;j<=n;j++)
{
a[i][j]*=b;
}
}
else if(d==1)
{
printf("Enter the row number to be multiplied\n");
scanf("%d",&c);
for(j=c,i=1;i<=m;i++)
{
a[i][j]*=b;
}
}
printf("matrix after multiplied\n");
for(i=1;i<=m;i++)
{
for(j=1;j<=n;j++)
{
printf("%d ",a[i][j]);
}
printf("\n");
}
return 0;
}
OUTPUT OF THIS CODING

Answer 2

I'm supposed to multiply a certain line (I specify what line exactly in the 4th argument of the function) of a given matrix by a number
Usually, "multiply a row of a matrix by a scalar" means to multiply every element of the row by a certain scalar value. That's not what the posted function does, it multiplies the index of the row by the passed argument:
void multiply_matrixNx100_line_by_scalar(int mNx100[][MAXCOLS100], int lines, int columns,
int line, int scalar) {
for (int i = 0; i < lines; i++) { // <-- Useless, the row is known
for (int j = 0; j < columns; j++) {
if(i == line){
printf("%d\n", mNx100[i*scalar][j] );
// ^^^^^^^^
}
}
printf("\n");
}
}
If the intent is to only print the modified row, the previous function could be rewritten as
void multiply_matrixNx100_line_by_scalar(int mNx100[][MAXCOLS100], int lines, int columns,
int line, int scalar) {
if (line < 0 || line >= lines)
return;
for (int j = 0; j < columns; j++) {
printf("%d\n", mNx100[line][j] * scalar);
}
printf("\n");
}
If instead the function is supposed to only modify the matrix, without printing it, we could use
mNx100[line][j] *= scalar;
Inside the loop, in place of the call to printf.