Ficaria assim:
char op[2];
for(i=0; i<casos; i++){
scanf("%d %s", &num, op);
if(op[0] == 'C')
coelhos = coelhos+num;
else if(op[0] == 'R')
ratos = ratos+num;
else if(op[0] == 'S')
sapos = sapos+num;
total = total+num;
}
per_c = (float)(coelhos*100.0)/total;
per_r = (float)(ratos*100.0)/total;
per_s = (float)(sapos*100.0)/total;