Expression must have constant value

[Ravello]

Hello, as the title says, I keep getting this error starting in line 14 and beyond. Int n gives me the error "expression must have constant value". I've researched this error message, but need a nudge in the right direction.

#include <iostream>
#include<sstream>
#include<string>
#include<algorithm>

using namespace std;

int main(){

int n, i, j;

cin >> n;

string first[n], last[n];

float gpa[n];

for(i = 0; i < n; i++){

cin >> last[i] >> first[i] >> gpa[i];

}

for(i = 0; i - n < 0; i = i + 1){

for(j = 0; j <= i; j = j + 1){

if(last[i] < last[j]){

string ftemp = first[i];

string ltemp = last[i];

float temp = gpa[i];

first[i] = first[j];

last[i] = last[j];

gpa[i] = gpa[j];

first[j] = ftemp;

last[j] = ltemp;

gpa[j] = temp;

}

else if(last[i] == last[j] && first[i] < first[j]){

string ftemp = first[i];

string ltemp = last[i];

float temp = gpa[i];



first[i] = first[j];

last[i] = last[j];

gpa[i] = gpa[j];

first[j] = ftemp;

last[j] = ltemp;

gpa[j] = temp;

}

}

}

cout << endl;

for(i = 0; i < n; i++){

cout << last[i] << " " << first[i] <<" " << gpa[i] << endl;

}

return 0;

}

[wildblue]

The compiler wants the n variable to be a constant (e.g. const int n = 20;) since you're using n to size arrays.

Since you're actually not going to know the size until the user enters it, you need to dynamically allocate the array with new- http://www.cplusplus.com/doc/tutorial/dynamic/ (and later deallocate with delete)

or - you use a vector instead of array.
http://www.cplusplus.com/reference/vector/vector/