Swap Strings (Without string.h)

#include <stdio.h>
int main()
{
    char a[100],b[100],temp[100];
    int i,la,lb;
    printf("Enter the first string: ");
    fgets(a,sizeof(a),stdin);
    printf("Enter the second string: ");
    fgets(b,sizeof(b),stdin);
    for(la=0;a[la]!='\0';la++);
    for(lb=0;b[lb]!='\0';lb++);
    for(i=0; i<lb; i++)
        temp[i] = b[i];
    for(i=0; i<la; i++)
        b[i] = a[i];
    for(i=0; i<lb; i++)
        a[i] = temp[i];
    a[lb-1]='\0';
    b[la-1]='\0';
    printf("String A is %s and String B is %s.",a,b);
}
//Output
//Enter the first string: Hello
//Enter the second string: Hi
//String A is Hi and String B is Hello.