程序代码：

#include <stdio.h>

 void main( ){ 
     char str[80];
     int i;
     printf ("String is: \n");
    
         scanf("%s",str);
         for (i=0; str[i]!='\0';i++)
         if (str[i]>='A' && str[i]<='Z')
         str[i]=str[i]+32;
         
            printf("Result is: %s\n",str);
}

程序代码：

#include <stdio.h>
void main() {
    char str[80];
    int i;
    printf("String is: \n");

    gets(str);
    for (i = 0; str[i] != '\0'; i++)
        if (str[i] >= 'A' && str[i] <= 'Z')
            str[i] = str[i] + 32;

    printf("Result is: %s\n", str);
}