C major 7 chord is usually written as either Cmaj7 or CM7 (Capital 'M' means major). Another thing is if you just see a letter like"C", this means just play a C major chord.
C minor 7 chord is either Cmin7, C-7, or Cm7 (lower case 'm' means minor)
C dominant chords are written as C7.
C augmented chord is either Caug or C+. Augmented 7th chords are written as CM7#5.
C diminished chord is either Cdim or C with a small circle next to it. If the circle has a slash through it, it's a half diminished chord.
Half diminshed 7th chords are usually written as Cm7b5. Diminshed seventh chords are either Cdim7 or C (small circle)7. (i.e. Co7)
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