Printing N X N matrix in spiral order

// OUTPUT : 1 2 3 4 5 10 15 20 25 24 23 22 21 16 11 6 7 8 9 14 19 18 17 12 13

#include<stdio.h>
#define MAX 5

void printSpiral(int a[][MAX],int n){
int loop = (n+1)/2;
int i,j,k;
for(k=0;k<loop;k++){
i=k;
j=k;
for(j=k;j<MAX-1-k;j++){
printf("%d ",a[i][j]);
}
for(i=k;i<MAX-1-k;i++){
printf("%d ",a[i][j]);
}
for(j=MAX-1-k;j>k;j--){
printf("%d ",a[i][j]);
}
for(i=MAX-1-k;i>k;i--){
printf("%d ",a[i][j]);
}
}
if(loop%2){
printf("%d",a[loop-1][loop-1]);
}
}

int main(){
        int a[][MAX] = {{1,2,3,4,5},
                      {6,7,8,9,10},
                      {11,12,13,14,15},
                      {16,17,18,19,20},
     {21,22,23,24,25}};
printSpiral(a,MAX);
        return 0;
}

Printing a N x N matrix using zigzag scanning algorithm

// Look here for zigzag scanning
// http://en.wikipedia.org/wiki/File:Zigzag_scanning.jpg
// INPUT : 4
// OUTPUT : 1 2 5 9 6 3 4 7 10 13 14 11 8 12 15 16

#include<stdio.h>
#include<stdlib.h>

int populateMatrix(int *A,int n){
int i,j;
int k=1;
for(i=0;i<n;i++){
for(j=0;j<n;j++){
*(A+i*n+j) = k++; 
}
}
}

void display(int *A,int n){
int i,j;
for(i=0;i<n;i++){
for(j=0;j<n;j++){
printf("%d ",*(A+n*i+j));
}
}
}

void goRight(int *A,int *i,int *j,int n){
int x = *i;
int y = *j;
printf("%d ",*(A+n*x+y));
*j = *j + 1;
}

void goDown(int *A,int *i,int *j, int n){
int x = *i;
int y = *j;
printf("%d ",*(A+n*x+y));
*i = *i + 1;
}

void goSW(int *A,int *i,int *j, int n){
int x = *i;
int y = *j;
while((y!=0) && (x!=n-1)){
printf("%d ",*(A+n*x+y));
x++;
y--;
}
*i = x;
*j = y;
}

void goNE(int *A,int *i,int *j, int n){
int x = *i;
int y = *j;
while((x!=0) && (y!=n-1)){
printf("%d ",*(A+n*x+y));
x--;
y++;
}
*i = x;
*j = y;
}

void goRightorDown(int *A,int *i,int *j,int n,int *prevrd){
if(*prevrd == 0){
goRight(A,i,j,n);
} else {
goDown(A,i,j,n);
}
*prevrd = !(*prevrd);
}

void goSWorNE(int *A,int *i,int *j,int n,int *prevsn){
if(*prevsn == 1){
goSW(A,i,j,n);
} else {
goNE(A,i,j,n);
}
*prevsn = !(*prevsn);
}

void zigzag(int *A,int n){
int i=0,j=0;
int prevrd = 0;
int prevsn = 1;
int k = 1;
int done = -1;
while(1 && n>1){
k=1;
while(1){
goRightorDown(A,&i,&j,n,&prevrd);
k++;
if(k==n){
done += 1;
break;
}
goSWorNE(A,&i,&j,n,&prevsn);
}
if(done){
break;
}
goSWorNE(A,&i,&j,n,&prevsn);
prevrd = !prevrd;
}
printf("%d ",*(A+n*i+j));
}

int main(){
int n;
scanf("%d",&n);
int *A = (int *)malloc(sizeof(int)*n*n);
populateMatrix(A,n);
zigzag(A,n);
free(A);
return 0;
}

Rotating a N X N matrix clockwise by 90 degrees

#include<stdio.h>
#define N 4

void display(int A[][N]){
int i,j;
for(i=0;i<N;i++){
for(j=0;j<N;j++){
printf("%d\t",A[i][j]);
}
printf("\n");
}
}

void rotate(int A[][N]){
int i,j;
int temp;
for(j=0;j<N/2;j++){
for(i=0;i<N-1-2*j;i++){
temp = A[j][i+j];
A[j][i+j] = A[N-1-i-j][j];
A[N-1-i-j][j] = A[N-1-j][N-1-i-j];
A[N-1-j][N-1-i-j] = A[i+j][N-1-j];
A[i+j][N-1-j] = temp;
}
}
}

int main(){
int A[N][N] = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
//int A[N][N] = {{1,2,3},{4,5,6},{7,8,9}};
printf("original matrix :\n");
display(A);
rotate(A);
printf("after rotating 90deg clockwise :\n");
display(A);
return 0;
}