I have a circular range of ascii values of a-z, from 97 to 122.
I am having trouble with decreasing the value, suppose the current value is 100 and i want to reduce it by 4 and it should return 122.
const startIndex=97
const endIndex=122
let increaseBy=reduceBy=5
let currentIndex=122
// increment
// this works
currentIndex=startIndex+((currentIndex-startIndex+increaseBy)%26)
// decrement
// need help
currentIndex=attempted_something_that_you_will_find_it_as_dumb
Modulo will walk your modulo-class as you wish, if you just keep adding your
startIndex + (currentIndex%26)
Now, you just make sure, your currentIndex want go below 0
you modify only the currentIndex
let startIndex = 97;
let currentIndex = 0;
for(let inc = 0; inc < 10; inc++) {
currentIndex += 5;
console.log(startIndex + (currentIndex%26));
}
for(let inc = 0; inc < 10; inc++) {
currentIndex -= 5;
console.log(startIndex + (currentIndex%26));
}
console.log("index will go below zero -> will break");
for(let inc = 0; inc < 10; inc++) {
currentIndex -= 5;
console.log(startIndex + (currentIndex%26));
}
console.log("index will stop at zero -> will not break");
for(let inc = 0; inc < 10; inc++) {
currentIndex = Math.max(0, currentIndex - 5);
console.log(startIndex + (currentIndex%26));
}
console.log("index will reset to modulo at zero -> will not break");
for(let inc = 0; inc < 10; inc++) {
currentIndex -= 5;
currentIndex = (currentIndex < 0) ? (26 + currentIndex) : currentIndex;
console.log(startIndex + (currentIndex%26));
}
The solution @thst gave works well. In short I'll mention my usage of the code
const startIndex = 97;
const endIndex = 122;
let currentIndex = 122;
//this value is varies according to the input i take
let increaseBy = (reduceBy = 5);
// increment
currentIndex = startIndex + ((currentIndex - startIndex + increaseBy) % 26);
// decrement
const milansConst=7;
currentIndex = startIndex + ((currentIndex - reduceBy + milansConst) % 26);
milansConst is a mysterious number (there is no logic to it) my friend came up with to get the decrement expression he made work.