C：在字符串中查找特定字符

Question

I am trying to write a program that searches for the first occurance of a specific character in a string. But no matter what character i type in the number the program gives back is the number of the last character.

int where (char *str, char ltr);

int main () {
    char word [80];
    char letter;
    printf("Type in a word: ");
    scanf("%s", word);
    printf("Type in a character: ");
    scanf("%s", letter);
    printf("%d", where(word, letter));
}

int where (char *str, char ltr){
    int i = 0;
    while(i < strlen(str)){
        if(ltr == str[i]){
            break;
        }
        i++;
    }
    return i;
}

Answer 1

The problem is that this here

scanf("%s", letter);

Is undefined behavior because it's expecting a pointer to a character, but you give it a character. The %s specifier is for reading strings, not single characters. Your compiler should warn you about a type mismatch here.

Instead, change it to this:

scanf(" %c", &letter);

%c is for reading in single characters, and with the leading space you make it ignore any leading whitespace in the input (such as the newline entered after you word).

You should also change scanf("%s", word); to scanf("%79s", word); in order to avoid undefined behavior when the user enters a very long word (this limits the word's length to your buffer's size).