在C中使用函数将字符串转换为大小写

Question

This is homework and this is the task I was given:
Prints the string in uppercase and lowercase
Splits the string on the middle and prints the two parts with " - " between Requirements:

Converting the string to upper and lower case must be done in functions. These functions must return nothing (void) and be called: string_upper, string_lower.
Do not use strlwr or strupr.

Note: The string length is always even.

Expected output (with the string you receive as input):

The string in uppercase is 'ABCDEFGH'
The string in lowercase is 'abcdefgh'
The string split in two is 'abcd - efgh'

I have managed to come up with something that works but it dosent use functions as requiered in the task. How can you do this with funtions?

I have looked around but I cant find any examples of converting strings to upper and lowercase using functions

#include<stdio.h>
#include<string.h>

int main() {

    char inputString[100], leftHalf[100], rightHalf[100];
    int length, mid, i, k;

    /* Read input string from user using gets */
    printf("Enter a string\n");
    gets(inputString);
    /* Find length of string using strlen function */
    length = strlen(inputString);

    mid = length/2;
    /* Copy left half of inputString to leftHalf */
    for(i = 0; i < mid; i++) {
        leftHalf[i]= inputString[i];
    }
    leftHalf[i] = '\0';

    /* Copy right half of inputString to rightHalf  */
    for(i = mid, k = 0; i <= length; i++, k++) {
        rightHalf[k]= inputString[i];
    }

    for(i=0;i<=strlen(inputString);i++)
    {
        if(inputString[i]>=65&&inputString[i]<=90)
            inputString[i]=inputString[i]+32;
    }
    printf("String in Lowercase: %s\n",inputString);
    /* To print string in upperCase*/
    for(i=0;i<=strlen(inputString);i++)
    {
        if(inputString[i]>=97&&inputString[i]<=122)
            inputString[i]=inputString[i]-32;
    }
    printf("String in Uppercase: %s\n",inputString);


    /* Printing left and right half of string */
    //printf("Left half : %s\n",leftHalf);
    //printf("Right half : %s\n",rightHalf);
    printf("%s-%s",leftHalf, rightHalf);

    return 0;
}

Answer 1

To create a function, just remove the code (eg the for-loop) to a function. Don't forget to declare auxiliary variables (eg int i). Like so

void string_upper (char *inputString)
{
    int i;
    for(i=0;i<=strlen(inputString);i++)
    {
        if(inputString[i]>=65&&inputString[i]<=90)
            inputString[i]=inputString[i]+32;
    }
}

And then in your main code, you call

string_upper (inputString);

instead of the for-loop that was there.

Do the similar for string_lower.

Answer 2

You can just put your code to convert the string to upper and lower case in separate functions. like this.

void string_upper (char* str) {
    for(int i=0; i<=strlen(str); i++) {
        if(str[i]>=97 && str[i]<=122)
            str[i]=str[i]-32;
    }
}

void string_lower(char* str) {
    //...
}

int main() {

    char inputString[100], leftHalf[100], rightHalf[100];
    int length, mid, i, k;

    //...

    /* call function to convert string to upper-case*/
    string_upper(inputString);
    printf("String in Uppercase: %s\n",inputString);

    /* call function to convert string to lower-case */
    string_lower(inputString);
    printf("String in Lowercase: %s\n",inputString);

    //...

    return 0;
}

Answer 3

If you're allowed to use tolower() and toupper() , this works:

#include <ctype.h>

// note unsigned char!
void string_upper( unsigned char *str )
{
    while ( *str )
    {
        *str = toupper( *str );
        str++;
    }
}

string_lower() is left as an exercise for the reader... ;-)