Ok understood. You can simplify this condition
C++:
if(kills[i] > kills[mostkills] || kills[i] == kills[mostkills] && dmg[i] > dmg[mostkills])
// To
if((kills[i] >= kills[mostkills]) && (dmg[i] > dmg[mostkills]))
And in this, first 2 lines are enough.
C++:
new mostkills = 0;
new mostknives = 0;
mostkills = 0;
mostknives = 0;
I have added more comments in the source. You can check, modify and update the plugin.
Note: Also I would recommend to learn the new syntax of sourcepawn. Currently you are mixing both new and old syntax. It's more easier to code and understand. I am attaching the code with some improvements and new syntax here. You can update the plugin.