使用整数指针的二维矩阵求和

Question

#include<stdio.h>
int main()
{
    int (*p)[3],i,j;
    int (*q)[3];
    int (*r)[3];
    printf("Enter 6 integers of first matrix:\n");
    for(i=0;i<2;i++)
        for(j=0;j<3;j++)
            scanf("%d",*(p+i)+j);
    printf("The matrix you have entered is:\n");
    for(i=0;i<2;i++)
    {
        for(j=0;j<3;j++)
    {
        printf(" %d ", *(*(p+i)+j));
    }
    printf("\n");
}
printf("Enter 6 integers of second matrix:\n");
for(i=0;i<2;i++)
    for(j=0;j<3;j++)
        scanf("%d",*(q+i)+j);

printf("The matrix you have entered is:\n");
for(i=0;i<2;i++)
{
    for(j=0;j<3;j++)
    {
        printf(" %d ", *(*(q+i)+j));
    }
    printf("\n");
}
for(i=0;i<2;i++)
{
    for(j=0;j<3;j++)
    {
        *(*(r+i)+j)=*(*(p+i)+j) + *(*(q+i)+j);
    }
}
printf("The summation matrix is:\n");
for(i=0;i<2;i++)
{
    for(j=0;j<3;j++)
    {
        printf(" %d ", *(*(r+i)+j));
    }
    printf("\n");
}


}

In this program I have declared 3 pointers to an array of 3 integers. when I execute, the first matrix works fine and displayed. However, when I enter integers for the second matrix it crashes. I tried a lot but it fails.

Answer 1

As you say you have a pointer , pointer should point to some memory location before writing something to it. In your case the pointer doesn't point to any valid memory location and hence the crash.

If you want a 2*3 matrix then you should be having

char *p[2];

p[0] =  malloc(sizeof(int) *3);

Then

p[i][j] is valid.

Similarly you should allocate memory for each pointers individually.