In this program of different operation on matrix the saddlepoint() function if not producing correct output. Why?

Question

I wrote this program to perform different operations on matrix using dynamic allocation, the function for finding the saddle point is not producing the correct output. Why?

#include<stdio.h>

int** inputmatrix(int **a,int r, int c)
{
    int i, j;
    a = (int**)malloc(r*sizeof(int));
    for(i=0; i<c; i++)
    {
        a[i] = (int*)malloc(sizeof(int));
    }
    printf("\n Input the Elements of the Matrix :");
    for(i=0; i<r; i++)
    {
        for(j=0; j<c; j++)
        {
            scanf("%d",&a[i][j]);
        }
    }
    return a;
}

int** add(int **a, int **b, int r, int c)
{
    int i,j;

    for(i=0; i<r; i++)
    {
        for(j=0; j<c; j++)
        {
            a[i][j] = a[i][j]+b[i][j];
        }
    }
    return a;
}
int** multiplication(int** a, int **b, int r1, int c1, int c2)
{
    int **c,i,j,k;
    c = (int**)malloc(r1*sizeof(int));
    for(i=0; i<c2; i++)
    {
        c[i] = (int*)malloc(sizeof(int));
    }
    for(i=0; i<r1; i++)
    {
        for(j=0; j<c2; j++)
        {
            c[i][j] = 0;
            for(k=0; k<c1; k++)
            {
                c[i][j] = c[i][j] + a[i][k]*b[k][j];
            }
        }
    }
    return c;
}

int minval(int **a, int r, int c)
{
    int i, min;
    min = a[r][0];
    for(i=0; i<c; i++)
    {
        if(a[r][i]<min)
        {
            min = a[r][i];
        }
    }
    return min;
}

int maxval(int **a, int r, int c)
{
    int i, max;
    max = a[0][c];
    for(i=0; i<r; i++)
    {
        if(a[i][c] > max )
        {
            max = a[i][c];
        }
    }
    return max;
}

void saddlepoint(int **a, int r, int c)
{
    int i, j, rpos, cpos, flag = 0,sp;
    for(i=0; i<r; i++)
    {
        for(j=0; j<c; j++)
        {
            if(a[i][j] == minval(a, i, j) && a[i][j] == maxval(a, i, j))
            {
                sp = a[i][j];
                flag = 1;
                rpos = i;
                cpos = j;
            }
        }
    }
    if(flag == 1)
    {
        printf("\n The Saddle point of the Matrix is found at position (%d,%d) value is %d ", rpos, cpos,sp);
    }
    else
    {
        printf("\n There is no saddle point in the Matrix ");
    }
}

int main()
{
    int **a, **b,r1,c1,r2,c2, i,j,ch;
    int **c;
    printf("\n enter your choice : \n1.Addition \n2.Multiplication \n3.Saddle Point \n4. Magic Square \n");
    scanf("%d",&ch);
    printf("\n enter the oder of matrix A :");
    scanf("%d%d",&r1,&c1);
    a = inputmatrix(a,r1,c1);
    switch(ch)
    {
        case 1:
                printf("\n enter the oder of matrix B :");
                scanf("%d%d",&r2,&c2);
                if(r1==r2 && c1==c2)
                {
                    b = inputmatrix(b,r2,c2);
                    a = add(a,b,r1,c1);
                    printf("\n the result of the addition of matrices is :");
                    for(i=0; i<r1; i++)
                    {
                        printf("\n");
                        for(j=0;j<c1; j++)
                        {
                            printf("%d\t",a[i][j]);
                        }
                    }
                }
                else
                {
                    printf("\n these matrices can't be added ");
                }
                break;
        case 2 :
                printf("\n Enter the Order of Matrix B :");
                scanf("%d%d",&r2,&c2);
                b = inputmatrix(b,r2,c2);
                if(c1 == r2)
                {


                    c = multiplication(a, b, r1, c1, r2);
                    for(i=0; i<r1; i++)
                    {
                        printf("\n");
                        for(j=0; j<c2; j++)
                        {
                            printf("%d\t",c[i][j]);
                        }
                    }
                }
                else
                {
                    printf("\n Sorry, These Matrices Can't be Multiplied ");
                }
                break;
        case 3 : saddlepoint(a,r1,c1);
                break;
        default : printf("\n Sorry, This is a Wrong Choice ");
            }
    return 0;
}

please let me know any logical error in my saddlepoint() function.

int minval(int **a, int r, int c)
{
    int i, min;
    min = a[r][0];
    for(i=0; i<c; i++)
    {
        if(a[r][i]<min)
        {
            min = a[r][i];
        }
    }
    return min;
}

int maxval(int **a, int r, int c)
{
    int i, max;
    max = a[0][c];
    for(i=0; i<r; i++)
    {
        if(a[i][c] > max )
        {
            max = a[i][c];
        }
    }
    return max;
}

void saddlepoint(int **a, int r, int c)
{
    int i, j, rpos, cpos, flag = 0,sp;
    for(i=0; i<r; i++)
    {
        for(j=0; j<c; j++)
        {
            if(a[i][j] == minval(a, i, j) && a[i][j] == maxval(a, i, j))
            {
                sp = a[i][j];
                flag = 1;
                rpos = i;
                cpos = j;
            }
        }
    }
    if(flag == 1)
    {
        printf("\n The Saddle point of the Matrix is found at position (%d,%d) value is %d ", rpos, cpos,sp);
    }
    else
    {
        printf("\n There is no saddle point in the Matrix ");
    }
}

Here in the saddlepoint() funtion i am checking that if any element of the 2D matrix is minimum in the row and simultaneously the maximum in the column , then that will be the saddle point. For this i'm calling the minval() and maxval() functions in the if condition of saddlepoint() fuction.

example of output : - enter your choice : 1.Addition 2.Multiplication 3.Saddle Point 4. Magic Square 3

enter the oder of matrix A :3 3

Input the Elements of the Matrix :1 2 3 4 5 6 7 8 9

The Saddle point of the Matrix is found at position (0,0) value is 1 amit@amit-HP-15-Notebook-PC:~$

Answer 1

#include <stdio.h>
#include <stdlib.h> // error #1: was missing this; required for malloc()

int** inputmatrix(int** a, int r, int c ) {

    int i,j;

    a = (int**)malloc(r*sizeof(int*)); // error #2: didn't have *
    for (i = 0; i < r; ++i) a[i] = (int*)malloc(c*sizeof(int)); // error #3: had i < c, error #4: didn't have c*
    printf("\n input the elements of the matrix : ");
    for (i = 0; i < r; ++i)
        for (j = 0; j < c; ++j)
            scanf("%d",&a[i][j]);
    return a;

} // end inputmatrix()

int** add(int** a, int** b, int r, int c ) {

    int i,j;

    for (i = 0; i < r; ++i)
        for (j = 0; j < c; ++j)
            a[i][j] = a[i][j]+b[i][j];
    return a;

} // end add()

int** multiplication(int** a, int** b, int r1, int c1, int c2 ) {

    int **c,i,j,k;

    c = (int**)malloc(r1*sizeof(int));
    for (i = 0; i < r1; ++i) c[i] = (int*)malloc(c2*sizeof(int)); // error #5: had i < c2, error #6: didn't have c2*
    for (i = 0; i < r1; ++i) {
        for (j = 0; j < c2; ++j) {
            c[i][j] = 0;
            for (k = 0; k < c1; ++k) c[i][j] = c[i][j] + a[i][k]*b[k][j];
        } // end for
    } // end for
    return c;

} // end multiplication()

int min_r(int** a, int r, int c ) { // suggestion: clarify the purpose of this function by renaming and adding comment: // min for row r across all columns 0:c-1

    int i,min;

    min = a[r][0];
    for (i = 0; i < c; ++i)
        if (a[r][i] < min)
            min = a[r][i];
    return min;

} // end min_r()

int max_c(int** a, int r, int c ) { // suggestion: clarify the purpose of this function by renaming and adding comment: // max for column c across all rows 0:r-1

    int i,max;

    max = a[0][c];
    for (i = 0; i < r; ++i)
        if (a[i][c] > max)
            max = a[i][c];
    return max;

} // end max_c()

void saddlepoint(int** a, int r, int c ) {

    int i,j,rpos,cpos,flag = 0,sp;

    for (i = 0; i < r; ++i) {
        for (j = 0; j < c; ++j) {
            if (a[i][j] == min_r(a,i,c) && a[i][j] == max_c(a,r,j)) { // error #7: was passing j instead of c into min_r(), error #8: was passing i instead of r into max_c()
                sp = a[i][j];
                flag = 1;
                rpos = i;
                cpos = j;
            } // end if
        } // end for
    } // end for
    if (flag == 1) // error #9: had flag = 1
        printf("\n the saddle point of the matrix is found at position (%d,%d) value is %d ",rpos,cpos,sp);
    else
        printf("\n there is no saddle point in the matrix ");

} // end saddlepoint()

int main(void) {

    int **a,**b,r1,c1,r2,c2,i,j,ch;
    int **c;

    printf("\n enter your choice : \n1. addition \n2. multiplication \n3. saddle point \n4. magic square \n");
    scanf("%d",&ch);
    printf("\n enter the order of matrix A : ");
    scanf("%d%d",&r1,&c1);
    a = inputmatrix(a,r1,c1);

    switch (ch) {
        case 1:
            printf("\n enter the order of matrix B : ");
            scanf("%d%d",&r2,&c2);
            if (r1 == r2 && c1 == c2) {
                b = inputmatrix(b,r2,c2);
                a = add(a,b,r1,c1);
                printf("\n the result of the addition of matrices is : ");
                for (i = 0; i < r1; ++i) {
                    printf("\n");
                    for (j = 0; j < c1; ++j)
                        printf("%d\t",a[i][j]);
                } // end for
            } else {
                printf("\n these matrices can't be added ");
            } // end if
            break;
        case 2:
            printf("\n enter the order of matrix B : ");
            scanf("%d%d",&r2,&c2);
            b = inputmatrix(b,r2,c2);
            if (c1 == r2) {
                c = multiplication(a,b,r1,c1,r2);
                for (i = 0; i < r1; ++i) {
                    printf("\n");
                    for (j = 0; j < c2; ++j)
                        printf("%d\t",c[i][j]);
                } // end for
            } else {
                printf("\n these matrices can't be multiplied ");
            } // end if
            break;
        case 3:
            saddlepoint(a,r1,c1);
            break;
        default:
            printf("\n this is a wrong choice ");
    } // end switch

    return 0;

} // end main()

Demo:

gcc a.c -o a;
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 1
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 1 2 3 4 5 6
##
##  enter the order of matrix B : 3 2
##
##  input the elements of the matrix : 7 8 9 10 11 12
##
##  the result of the addition of matrices is :
## 8 10
## 12  14
## 16  18
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 1
##
##  enter the order of matrix A : 1 1
##
##  input the elements of the matrix : 3
##
##  enter the order of matrix B : 2 1
##
##  these matrices can't be added
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 2
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 1 2 3 4 5 6
##
##  enter the order of matrix B : 2 1
##
##  input the elements of the matrix : 10 20
##
## 50
## 110
## 170
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 2
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 1 2 3 4 5 6
##
##  enter the order of matrix B : 1 2
##
##  input the elements of the matrix : 1 2
##
##  these matrices can't be multiplied
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 3
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 1 2 3 4 5 6
##
##  the saddle point of the matrix is found at position (2,0) value is 5
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 3
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 6 5 4 3 2 1
##
##  the saddle point of the matrix is found at position (0,1) value is 5
./a;
##
##  enter your choice :
## 1. addition
## 2. multiplication
## 3. saddle point
## 4. magic square
## 3
##
##  enter the order of matrix A : 3 2
##
##  input the elements of the matrix : 1 2 2 1 1 2
##
##  there is no saddle point in the matrix