The loop wont run for a specific condition in C programming - c

Question

So our teacher gave us a assignment on making a C program to find the solution of linear equation by gauss-jordan method and so I did. It was told that we need to make the program so that it can compute equation having upto 4 variable....The problem i am facing is I want to make it such that the user can use it as many time as he wants but for some random invisible reason when i calculate eqn of 4 variable it gives the answer but the loop ends there however the eqn having 3 variables and below works totally fine.
The CODE is given please HELP ME. Copy-paste to a compiler :)
#include <stdio.h>
#include <math.h>
int main()
{ printf("\t\t\t\t\t\t\t\tPROGRAM TO FIND SOLUTION FOR LINEAR EQUATION UPTO 4 VARIABLE BY GAUSS JORDAN METHOD\n\n\n");
char op = 'y';
while(op =='y')
{
int n;
char var[] = {'x','y','z','w','t'}; //ASSIGNING THE VARIABLE TILL 4
printf("Enter no. of variable : ");
scanf("%d",&n); //ASKING FOR VARIABLE TO KNOW THE NUMBER OF EQUATION AND CALCULATE DIMENSION OF MATRIX
printf("\n\nTHE EQUATION IS IN FORMAT OF ax+by+cz....=k\n\n\n");
float Mat[n][n+1]; //MATRIX DECLARATION
int i,j;
if(n<5)
{
//TAKING INPUT FOR MATRIX
for(i=0;i<n;i++)
{
for(j=0;j<n;j++)
{
printf("Enter the %c coefficient of equation %d : ",var[j],i+1);
scanf("%g",&Mat[i][j]);
}
printf("Enter the constant of equation %d : ",i+1);
scanf("%g",&Mat[i][n]);
printf("\n\n");
}
//PRINTING ALL EQUATIONS
printf("GIVEN EQUATIONS : \n\n");
for(i=0;i<n;i++)
{
for(j=0;j<n+1;j++)
{
if(j<n-1)
{
printf("%g%c + ",Mat[i][j],var[j]);
}
else if(j == n-1)
{
printf("%g%c = ",Mat[i][j],var[j]);
}
else if(j == n)
{
printf("%g",Mat[i][j]);
}
}
printf("\n");
}
//PRINTING THE INITIAL MATRIX
printf("\nTHE INITIAL MATRIX : \n\n");
for(i=0;i<n;i++)
{
for(j=0;j<n+1;j++)
{
if(j==n-1)
{
printf("%g | ",Mat[i][j]);
}
else
{
printf("%g ",Mat[i][j]);
}
}
printf("\n");
}
//SIMPLIFYING THE MATRIX FOR SMOOTHER PROCESS
int change[n+1];
if(Mat[0][0] == 0)
{
int num;
for(int k=0;k<n;k++)
{
if(Mat[k][0]!=0)
{
num = k;
}
}
for(int k=0;k<n+1;k++)
{
change[k] = Mat[0][k];
Mat[0][k] = Mat[num][k];
Mat[num][k] = change[k];
}
}
for(int k=0;k<n+1;k++)
{
Mat[0][k] == Mat[0][k]/Mat[0][0];
}
//PERFORMING GOS JORDAN METHOD
for(int k = 0;k<n-1;k++)
{
for(int i = 1;i<n;i++)
{
float c = Mat[i+k][0+k]/Mat[0+k][0+k];
for(int j = 0;j<n+1;j++)
{
Mat[i+k][j+k] -= c*Mat[0+k][j+k];
}
}
}
//2ND GAUSSIAN CYCLE
for(int k = n;k>0;k--)
{
for(int i = 1;i<n;i++)
{
float c = Mat[k-i-1][k-1]/Mat[k-1][k-1];
for(int j = n;j>-1;j--)
{
Mat[k-i-1][j] -= c*Mat[k-1][j];
}
}
}
//SIMPLIFYING
for(i=0;i<n;i++)
{
for(j=n;j>-1;j--)
{
Mat[i][j] = Mat[i][j]/Mat[i][i];
if(Mat[i][j]== -0)
{
Mat[i][j] = 0;
}
}
}
printf("\n\n\n");
//PRINT END PRODUCT
printf("MATRIX AFTER APPLYING GAUSS JORDAN METHOD : \n\n");
for(i=0;i<n;i++)
{
for(j=0;j<n+1;j++)
{
if(j==n-1)
{
printf("%g | ",Mat[i][j]);
}
else
{
printf("%g ",Mat[i][j]);
}
}
printf("\n");
}
//PRINTING THE SOLUTION OF THE LINEAR EQUATION
printf("\n\nTHE SOLUTION FOR THE GIVEN LINEAR EQUATIONS ARE\n\n");
for(i=0;i<n;i++)
{
printf("%c = %g\n",var[i],Mat[i][n]);
}
printf("Do You want to continue? (y/n) : ");
scanf("\n%c",&op);
}
}
//THE END
}
Why wont the while loop run on a specific 4 variable condition.