When I Was Your Man by Bruno Mars is in C at 72 beats per minute and runs 3:30 across 38 bars. It uses 12 chords — D7, Dm7, C, G, Am, Dm, G7, Em, and a few more. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? When I Was Your Man guitar melody tab.