C++ :: Increasing Integers Automatically Within Two Dimensional Array

I am new to programming all together but i have been writing a program in c++ and im coming up against an issue with my array.

#include<iostream>
#include<iomanip>
#include<string>
using namespace
int main () {
int a ;
int b ;
char answer ('Y') ;

[Code] ....

I am trying to get the program to increase say year one by 1 when the condition is met i have tried

if ( a >= 70 && a <= 100 && b == 1)
{grade [0][0] = 0 + 1;}

and

for (grade[0][0] = 0 ; a >= 70 && a <= 100 && b == 1 ; grade [0][0]++)
{grade [0][0]= 0 + 1 ;}

Now all that i want is that the array will take the information from int a and int b and then add 1 to the appropriate part of the array . I have tried putting it in deferent places but its not working for ether. the program will run but it will not add to the array.