function if in while block in language C

Question

someone could help, I trying to code, a program to read a char, and output 1 to lower char, 2 to Upper and -1 if it's not a letter. The program should keep working until the input be a Zero

I can't understand why the following code; keeping print -1 in all situations of the "if" block;

I try two ways:

first try:

#include <stdio.h>

int main() {
    char entrada = 'x';
    
    while (entrada != 48) {
        scanf("%c", &entrada);
            
        if (entrada > 96 && entrada < 123) {
            printf("%d\n", 1);
        } else if (entrada > 64 && entrada < 91) {
            printf("%d\n", 2); 
        } else {
            printf("%d\n", -1);
        }     
    }
    return 0;
}

second try:

#include<stdio.h>

int main() {
    char entrada = 'x';
    int teste;
    
    while (entrada != 48){
        scanf("%c", &entrada);
            
        if (entrada > 96 && entrada <123){
            printf("%d\n", 1);
            continue;
        } else {
            if (entrada > 64 && entrada < 91) {
                printf("%d\n", 2);
                continue;
            } else if (entrada <= 64 || (entrada >= 91 && entrada <= 96) 
                       || entrada >= 123 ) {
                printf("%d\n", -1);
                continue;
            }
        }
    }

    return 0;
}

Answer 1

When your program (either of them) executes scanf("%c", &entrada);, scanf reads a single character.

When you type “a” and press Enter or Return, two characters are sent to your program: “a” and a new-line character.

When your program reads “a“, it prints “1”.

When your program reads the new-line character, it prints “-1”.

So, as long as you enter a character and press Enter or Return, your program prints two numbers: one for the first character and one for the new-line character.