Find second highest number without using array [duplicate]

Answer 1

Bad check of value in your way. For example, like this

#include 

#define EOI -1 //End Of Input

int main(void){
    int input, first, second;

    first = second = EOI;

    while(1){
        if(1 != scanf("%d", &input)){
            fprintf(stderr, "invalid input!\n");
            return -1;
        }
        if(input == EOI)
            break;
        if(first == EOI){
            first = input;
        } else if(first <= input){
            second = first;//slide
            first = input;
        } else if(second == EOI || second < input){
            second = input;
        }
    }
    if(second == EOI){//first == EOI || second == EOI
        fprintf(stderr, "No valid value is entered more than one!\n");
        return -2;
    }
    printf("%d\n", second);
    return 0;
}