How can I change a string only 4 times using differences between ints?

I have 4 differences and using the below code I would like to change a string of four characters just 4 times in the order of the code below:

    var dif1 = it1 - it5;
    var dif2 = it2 - it6;
    var dif3 = it3 - it7;
    var dif4 = it4 - it8;

    if (dif1 < 0.0) dif1 = -dif1;
    if (dif2 < 0.0) dif2 = -dif2;
    if (dif3 < 0.0) dif3 = -dif3;
    if (dif4 < 0.0) dif4 = -dif4;

    var change = 0 

    // Difference 1
    if ((dif1 < 13)&&(dif1 == fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    change = 1
    }
    // Difference 2
    else if ((dif2 < 13)&&(dif2 == fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    change = 1
    }
    // Difference 3
    else if ((dif3 < 13)&&(dif3 == fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    change = 1
    }
    // Difference 4
    else if ((dif4 < 13)&&(dif4 == fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    change = 1
    }

    if ((dif1 + dif2) <13) {
    if (change == 1) {
    }
    change = 2;
    }

    else if ((dif2 + dif3) <13) {
    if (change == 1) {
    }
    change = 2;
    }

    else if ((dif3 + dif4) <13) {
    if (change == 1) {
    }
    change = 2;
    }

    else if ((dif1 + dif4) <13) {
    if (change == 1) {
    }
    change = 2;
    }

    if ((dif1 + dif2 + dif3) <13) {
    if (change == 1) {
    }       
    else if (change == 2) {
    }        
    change = 3;
    }

    else if ((dif2 + dif3 + dif4) <13) {
    if (change == 1) {
    }        
    else if (change == 2) {
    }
    change = 3;
    }

    else if ((dif3 + dif4 + dif1) <13) {
    if (change == 1) {
    }        
    else if (change == 2) {
    }
    change = 3;
    }

    else if ((dif4 + dif1 + dif2) <13) {
    if (change == 1) {
    }        
    else if (change == 2) {
    }
    change = 3;
    }

    if ((dif1 < 13)&&(dif1 != fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    if (change == 1) {
    }
    else if (change == 2) {
    }
    else if (change == 3) {
    change = 4;
    }

    else if ((dif2 < 13)&&(dif2 != fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    if (change == 1) {
    }
    else if (change == 2) {
    }
    else if (change == 3) {
    }
    change = 4;
    }

    else if ((dif3 < 13)&&(dif3 != fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    if (change == 1) {

    else if (change == 2) {

    else if (change == 3) {

    change = 4;
    }

    else if ((dif4 < 13)&&(dif4 != fmin(dif1, fmin(dif2, (fmin(dif3, dif4)))))) {
    if (change == 1) {
    }
    else if (change == 2) {
    }
    else if (change == 3) {
    }
    change = 4;
    }

The question is mostly if this code can be transformed in a function and if so how can I let the string be modified just 4 times?