How to check if one or more string has uppercase/lowercase initial character (C Language)

Question

#include <stdio.h>

char leitura(const char *str){
    int i, resultado;

    for(i = 0; str[i] != '\0'; i++){
        if(str[0] >= 'A' && str[0] <= 'Z' && str[' ' + 1] >= 'A' && str[' ' + 1] <= 'Z'){
            resultado = 1;
        }else{
            resultado = 0;
        }
    }
    printf("O resultado eh: %d", resultado);
    return resultado;
}

int main(){
    char str[30];

    fgets(str, 30, stdin);
    leitura(str);

    return 0;
}

Answer 1

For starters, str[' ' + 1] doesn’t make sense. It doesn’t do what you expect (probably you thought it would be a position after space, or something?) - actually, char and int are sort of "interchangeable" in C (char, despite the name, is a numerical type). In this case, the character ' ' is the blank, whose code in ascii table is 32, so you’re actually trying to access position 33 of str:

// imprimir como char
printf("%c\n", ' ' + 1); // !
// imprimir como inteiro
printf("%d\n", ' ' + 1); // 33

And how str was declared with 30 positions, trying to access a position beyond this limit generates a undefined behavior (read more about here, here and here).

Another detail is that in loop you are always checking str[0] (the first position of str) but actually you should use the i, because that’s what it’s for: to iterate through the characters of str.

---

Also, the title is confused. If you want to check the string "uppercase/lowercase initial character", wouldn’t it be enough to check the first character? Then you wouldn’t even need a loop:

char str[30];
fgets(str, 30, stdin);

if ('A' <= str[0] && str[0] <= 'Z') {
    // primeiro caractere é letra maiúscula
} else if ('a' <= str[0] && str[0] <= 'z') {
    // primeiro caractere é letra minúscula
} else {
    // primeiro caractere não é letra maiúscula nem minúscula
}

Or - based on first version of the title - you want to see if there’s any word that starts with uppercase?

In this case, a simple way is to check, for each character, if in addition to being a capital letter, the previous character is not a letter. Something like this:

int maiuscula(char c) {
    return 'A' <= c && c <= 'Z';
}

int letra(char c) {
    return ('a' <= c && c <= 'z') || maiuscula(c);
}

int main() {
    char str[30];
    fgets(str, 30, stdin);
    int encontrou = 0;
    for (int i = 0; str[i] != '\0'; i++) {
        if (maiuscula(str[i]) && (i == 0 || !letra(str[i - 1]))) {
            encontrou = 1;
            break; // se já encontrei, nem precisa continuar procurando
        }
    }
    if (encontrou) {
        printf("Encontrei\n");
    } else{
        printf("Não encontrei\n");
    }

    return 1;
}

If I find a word that starts with uppercase, I interrupt the loop, because I understood that finding one is enough and you don’t have to keep looking for others.

I created functions to check if a char is a capital letter, or any letter. In for, the verification is done in the if, which verifies two conditions:

• maiuscula(str[i]): checks if the current letter is uppercase
• i == 0 || !letra(str[i - 1]): checks if it is the first character of the string (i == 0), or if the previous one is not letter (the operator || is the "or", and the operator ! is the negation, then !letra(str[i - 1]) checks if the character in the position i - 1 is not a letter)

Both of the above conditions must occur to enter the if, because I used the operator && ("and"). That is, if it is not a capital letter, or if it is, but it is not the first or the previous one is a letter, it does not enter the if.

Thus the code becomes more generic than if we consider only spaces to separate words (the string can be something like "-blablabla,Etc" for example - as no detail has been specified in this regard, it is better to assume that the user can type "anything").

---

In another answer (currently deleted) it was suggested that instead of the for, using pointer arithmetic. That is, something like this:

int maiuscula(char c) {
    return 'A' <= c && c <= 'Z';
}

int letra(char c) {
    return ('a' <= c && c <= 'z') || maiuscula(c);
}

int temInicialMaiuscula(char *str) {
    int i = 0;
    while (*str) {
        if ((i++ == 0 || !letra(*(str - 1))) && maiuscula(*str)) {
            return 1; // se já encontrei, nem precisa continuar procurando
        }
        str++;
    }
    return 0;
}

int main() {
    char str[30];
    fgets(str, 30, stdin);
    if (temInicialMaiuscula(str)) {
        printf("Encontrei\n");
    } else{
        printf("Não encontrei\n");
    }

    return 1;
}

Which basically does the same thing as the previous version (the main logic is the same). The difference is that instead of making a for by the indices of the string, we used pointer arithmetic to make each iteration str point to the next character. To better understand, I suggest reading here.

---

Another option is to reverse the logic: first I see if the current character is not letter, and if not, I see if the next one is uppercase:

int temInicialMaiuscula(char *str) {
    while (1) {
        if (! letra(*str)) { // se caractere atual não é letra, verifica o próximo
            str++;
            if (! *str) // chegou no final da string
                return 0;
            if (maiuscula(*str))
                return 1; // encontrei palavra que começa com maiúscula, retorna
        } else str++;
    }
    return 0;
}

Answer 2

Your show is really complicated, and I really don’t get it. You can use something simple like

int inicial_minuscula(const char* str)
{
   return (((*str) >= 'a') && ((*str) <= 'z'));
};

And

int inicial_maiuscula(const char* str)
{
    return (((*str) >= 'A') && ((*str) <= 'Z'));
};

Only