求大神指教！！

Question

 求大神指教，哪错了#include<stdio.h>int add(int a,int b){ int c; c = a+b;return (c);}int sub(int d,int e){ int f; f = d-e;return (f);}main(){ int a,b,c; a = 20; b = 10;    c = add(a,b);    printf("%d+%d=%d",a,b,c);    int d,e,f; d = 20; e = 10;    f = add(d,e);    printf("%d-%d=%d",d,e,f);}