Assuming you can index circularly and auto letter to integer mapping:
openStrings='E','A','D','G','B','E';
notes='A','A#','B','C','C#','D','D#','E','F','F#','G','G#';
fret[6][24]
for( i=0; i<6; i ) {
for( j=0; j<24; j ) {
fret[i][j] = notes[ openStrings[i] j ]
}
}