入力を安全に受け取る ref: http://qiita.com/memememomo/items/34e86058872b2fe508bb

main.c

#include <stdio.h>

int main()
{
    char buf[80];
    int a, b;

    fgets(buf, 80, stdin);
    sscanf(buf, "%d %d", &a, &b);

    printf("%d + %d = %d\n", a, b, a+b);

    return 0;
}