Addtionally challenged

i want to add and subtract a number to the var currentProj
heres my logic

start value for currentProj is 0

code on prevbtn
currentProj -= 1; // should subtract 1 from currentProj

when prevbtn is clicked the variable currentProj
goes from 0 to -1 to -2 to -3…etc with every click. this is fine once i set my limits at zero

code on nextbtn
currentProj +=1; // should add 1 to currentProj

when nextbtn is clicked the variable currentProj
goes from 0 to 01 to 011 to 0111…etc with every click. this is whack

I’ve wasted an hour trying to work around this and just need help

confused,
JW