Difference between ' & "

[Atomic_Sheep]

I have a basic program:

char chTest;
    chTest = 'a';
    qDebug() << chTest;

char chTest;
    chTest = 'a';
    qDebug() << chTest;

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However if I use "a", it spits out an error at me - 47: error: invalid conversion from 'const char*' to 'char'

What does that error mean? And why does it occur?