Pointers predict the output

Question

#include <stdio.h>

void main (void){
    int mat [5][5],i,j;
    int *p;            
    p = &mat [0][0];
    for (i=0;i<5;i++)
        for (j=0;j<5;j++)
            mat[i][j] = i+j;
    printf ("%d\t", sizeof(mat));   i=4;j=5;
    printf( "%d", *(p+i+j));
}

Can somebody help me with the output of this snippet . I get it the sizeof(mat) will print 50 . But help me with second printfc

What is your question exactly? Are you asking what the output is? Why don't you just run it? — JBentley, Jul 24 '14 at 17:43
Also, `void main (void){//...}` is not valid C++, so your code has undefined behaviour. See [Main's Signature in C++](http://stackoverflow.com/q/1621574/1227469) — JBentley, Jul 24 '14 at 17:47
Does not looks much at all like C++ for the rest of it, either. — crashmstr, Jul 24 '14 at 17:48
On [ideone](http://ideone.com/AVICGW) the output is 100 and 5 respectively (after fixing the code to make it compile). — JBentley, Jul 24 '14 at 17:52
`%d` is not suited for printing `size_t` (which is the result of the `sizeof` operator.) — The Paramagnetic Croissant, Jul 24 '14 at 18:19

score 2 · Answer 1 · edited Jul 24 '14 at 17:49

2

Try changing this second statement to:

printf("%d",*(p)+i+j );

I'm guessing you mean to print the sum of the value pointed at by p and the values stored in i and j

edited Jul 24 '14 at 17:49

Norman Gray

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answered Jul 24 '14 at 17:42

kwierman

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score 2 · Accepted Answer · answered Jul 24 '14 at 17:55

*(p+i+j) will print the value stored at the address p + i*sizeof(int) + j*sizeof(j)

As array are stored in a linear way in the stack and i equals 4 and j equals 5 this will show the value of the 9th int of the array hence mat[1][4] which is equal to 5

Also for the result of sizeof(mat), it will be 5*5*sizeof(int). I assume here your int are stored on two bytes because you said it would print 50 but it totally depends on your computer. It is more usually 4 bytes long on todays computer so it could also print 100.

Pointers predict the output

2 Answers2