Capitalizing certain chars in a string in C -

i'm looking way convert upper case letters lower case letters user inputted string. problem conditional ignored, , every character changed, not upper case ones. record tried converting chars ints using atoi encountered same issue above.

#include <stdio.h> #include <stdlib.h> #include <string.h>  int main() {     char letter[100];     scanf("%s", letter);     int i;     for(i=0; letter[i]!='\0'; i++){         if((letter[i]>='a')||(letter[i]<='z')){             letter[i]=letter[i]+32;         }     }     printf("%s", letter);     return 0; } 

i suggest using library functions, islower(), isupper(), toupper() , tolower() this. in case, this:

for(i = 0; < strlen(letter); i++) {     letter[i] = tolower(letter[i]); }