Conversion of uppercase and lowercase letters, C language implementation

★ Write a program, you can always receive keyboard characters, if it is lowercase characters on the output corresponding uppercase characters, if you receive uppercase characters, the output corresponding lowercase characters, if the number is not output.

#include <stdio.h>int main () {char c;while ((c = GetChar ()) = EOF) {if ((+ <= c) && (c <= 91))/ /uppercase converted to lowercase letter {printf ("%c", C + 32);} else if ((97<= c) && (C <= 123))//lowercase letters are converted to uppercase {printf ("%c", c-32);} else if ((<= c) && (C <= 56))//The number received is not processed {NULL;}            else{printf ("\ n"); Re-enter}}return 0 from the new line after the result is obtained;}

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Conversion of uppercase and lowercase letters, C language implementation