关于 C 编程中的冲突类型错误

Question

can anyone help me to find the why I am getting conflicting type of error in in the toLower(char letter) function.

#include <stdio.h>

int main()
{
    char letter;
    printf("Enter the upper case letter..!!");
    scanf("%c", &letter);
    char new_letter = toLower(letter);

    printf("The new letter is %c " , new_letter);
   return 0;
}
char toLower(char letter)
{
    int distance = (int)'a' - (int)'A'; // Calculating the distance between letters...

    char new_letter = letter + (char) distance;

    return new_letter;
}

Answer 1

In C, you must always declare the function prior to calling it. This is what Tom Karaz has pointed out in a comment to your post.

There are two possible solutions.

Solution 1:

#include <stdio.h>
char toLower(char letter)
{
    int distance = (int)'a' - (int)'A'; // Calculating the distance between letters...

    char new_letter = letter + (char) distance;

    return new_letter;
}
int main()
{
    char letter;
    printf("Enter the upper case letter..!!");
    scanf("%c", &letter);
    char new_letter = toLower(letter);

    printf("The new letter is %c " , new_letter);
   return 0;
}

Solution 2: This solution makes use of function prototyping. That is on the second line I have taken the function signature and declared that prior to where I invoke a function call. The function prototype and the function signature must be identical.

#include <stdio.h>
char toLower(char letter);  // function prototype
int main()
{
    char letter;
    printf("Enter the upper case letter..!!");
    scanf("%c", &letter);
    char new_letter = toLower(letter);
    printf("The new letter is %c " , new_letter);
   return 0;
}

char toLower(char letter)
{
    int distance = (int)'a' - (int)'A'; // Calculating the distance between letters...

    char new_letter = letter + (char) distance;

    return new_letter;
}