为什么 scanf function 在列表中看起来较低，但首先评估它？

Question

When I run this code, and I press 1 at the end of it, instead of printing out message one, it just goes straight to scanf, and only after I enter in my input does it print message one.

#include <stdio.h>

void main() {
    int year;
    int decision;
    printf( "\nThis program tells the user what the GDP per capita of post-independence South Sudan was in a given year. The availability of a figure for a certain year is subject to the limitations of the data that was provided by the World Bank. " );
point_one :
    printf( "Enter a year below to get a figure for that year.\n\n" ); // message one
    scanf( "%d" , &year );
    if(2011 > year || year > 2015 )
        printf( "\nThe figure for that year is unavailable.\n" );
    else if( year == 2011 )
        printf( "\n1,516.40 USD\n" );
    else if( year == 2012 )
        printf( "\n1,179.40 USD\n" );
    else if( year == 2013 )
        printf( "\n1,779.47 USD\n" );
    else if( year == 2014 )
        printf( "\n1,322.82 USD\n" );
    else if( year == 2015 )
        printf( "\n1,119.65 USD\n" );
    printf( "\nDo you want to try again or leave?\n\n" );
    scanf ( "%d\n\n" , &decision );
    if ( decision == 1 )
        goto point_one;
    else return;
}

Answer 1

1. void main is invalid.
2. Do not use goto . There are some circumstances when using goto is reasonable but IMO beginners should not use it at all.
3. Check return values of scanf.
4. Use correct formats ("\n\n") was nor correct
5. In this case I would use swich instead of if s

int main(void) {
    int year;
    int decision;
    printf( "\nThis program tells the user what the GDP per capita of post-independence South Sudan was in a given year. The availability of a figure for a certain year is subject to the limitations of the data that was provided by the World Bank. " );
    do{
        printf( "Enter a year below to get a figure for that year.\n\n" ); // message one
        if(scanf( "%d" , &year ) != 1) {/* error handling */ exit(2);}
        switch(year)
        {
        case 2011:
            printf( "\n1,516.40 USD\n" );
            break;
        case 2012:
            printf( "\n1,179.40 USD\n" );
            break;
        case 2013:
            printf( "\n1,779.47 USD\n" );
            break;
        case 2014:
            printf( "\n1,322.82 USD\n" );
            break;
        case 2015:
            printf( "\n1,119.65 USD\n" );
            break;
        default:
            printf( "\nThe figure for that year is unavailable.\n" );
            break;
        }
        printf( "\nDo you want to try again or leave?\n\n" );
        if(scanf ( "%d" , &decision ) != 1) {/* error handling */ exit(3);}
    }while(decision == 1);
}

https://godbolt.org/z/793PdYdrh

But instead of switch and ifs you can use table and make your code much better (for example it will be very easy to add more years).

int main(void) {
    int year;
    int decision;

    unsigned data[] = {151640, 117940, 177947, 132282, 111965};
    printf( "\nThis program tells the user what the GDP per capita of post-independence South Sudan was in a given year. The availability of a figure for a certain year is subject to the limitations of the data that was provided by the World Bank. " );
    do{
        printf( "Enter a year below to get a figure for that year.\n\n" ); // message one
        if(scanf( "%d" , &year ) != 1) {/* error handling */ exit(2);}
        if(year < 2011 || year > 2015) printf( "\nThe figure for that year is unavailable.\n" );
        else printf( "\n%d.%d USD\n", data[year - 2011] / 100, data[year - 2011] % 100);

        printf( "\nDo you want to try again or leave?\n\n" );
        if(scanf ( "%d" , &decision ) != 1) {/* error handling */ exit(3);}
    }while(decision == 1);
}