c++ - while loop keeps running -

so code snippet :

double numericalmethod::splinelinearinterpolation(){  int n, i=0; double x[100], y[100], s[100],a; cout << "enter no. of sample points : \n"; cout << "\n"; cin  >> n; cout << "\n"; cout << "enter values of x , corresponding functional value y :  \n"; cout << "\n"; cout << "x | y \n"; (i=0; i<n; i++){     cin >> x[i] >> y[i]; } cout << "\n"; cout << "enter value of  x calculate estimated value of y : \n "; cout << "\n"; cin  >> a; while (a<x[0] or a>x[n]){     cout << "the selected value of x must belong domain [" << x[0] << "," << x[4] << "] \n" ;     cout << "\n";     cout << "reenter value of x please : ";     cout << "\n";     cin  >> a; } cout << "\n";  (i=0; i<n-1; i++){    s[i]=y[i] + ((y[i+1]-y[i])/(x[i+1]-x[i]))*(a-x[i]);    if (a>=x[i] , a<=x[i+1])        cout << "s[" << << "] =" << s[i] << "   when " << x[i] << " <= x <=" << x[i+1] <<endl;  } return 0; 

}

x array

when ever program enters loop never exits it

although when switch x[0] , x[n] constant numbers runs

any ideas? , thanks

you reading in way:

for (i = 0; < n; i++) {   cin >> x[i] >> y[i]; } 

array x have values in positions: [0, n-1]

but in while:

while (a < x[0] or > x[n] ){ 

your trying access position n of array, random number if not initialized.