C 编程 - 不能多次调用函数

Question

I'm having trouble calling the function more than one time in my C program. The gist of the assignment is to replace the whitespaces in a sentence inputted from the user and replace it with a different character. For some reason, the program will call the same first function multiple times. I tried putting the strlen(x) in a variable inside my function, but I'm not very well versed in the C language, so I decided to leave it out of my code.

#include <string.h>

void display(char x[], char y);

void main(){
    //Do not change this function
    char a[100];
    printf("Enter a sentence\n");
    gets(a);
    display(a, '*');        //To replace every space by *
    display(a, '-');        //To replace every space by -
    display(a, '+');        //To replace every space by +
}

void display(char x[], char y){
    for(char i = 0; i < strlen(x); i++) {
        if(x[i] == ' ') {
            x[i] = y;
        }
    }
    printf("%s\n", x);
}

Answer 1

It does not "call the same first function". You change the value of your string inside the function, so after the first run of the function the string does not have spaces. Therefore the second and third call print the string unchanged:

void display(char x[], char y){
    for(char i = 0; i < strlen(x); i++) {
        if(x[i] == ' ') {
           // this happens only upon first call! 
           x[i] = y;
       }
    }
    printf("%s\n", x);
}

Edit : to fix the issue, for example see the comment Ring Ø added and follow the advice