“先声明(定义),后使用” #include " stdio. h include " stdio. h" int sum(int b, int a) int sum (int, int)i main () a a +b: b a+ b in七 1,b=2 return ai c= sum(a, b)i printf("sum d\n",c)i main o int sum(int b, int a) in七a 1,b c sum(a, b) a= a bi printf ("sum =d\n",c) b s a b: re七urna 电子科技大学通信与信息工程学院电子科技大学通信与信息工程学院 “先声明（定义），后使用” #include "stdio.h" int sum(int b, int a) { a = a + b; b = a + b; return a; } main() { int a = 1, b = 2, c; c = sum(a, b); printf("sum = %d\n",c); } #include "stdio.h" int sum(int, int); main() { int a = 1, b = 2, c; c = sum(a, b); printf("sum = %d\n",c); } int sum(int b, int a) { a = a + b; b = a + b; return a; }