415. 字符串相加c

void reverse(char* num1, int n){
    int head=0,tail=n-1;
    while(head<=tail){
        char c=num1[head];
        num1[head]=num1[tail];
        num1[tail]=c;
        head++;
        tail--;
    }
}

int max(int i,int j){
    if(i>j) return i;
    return j;
}

char * addStrings(char * num1, char * num2){
    int n1=strlen(num1),n2=strlen(num2);
    char* temp=(char*)malloc(sizeof(char)*15000);
    for(int i=0;i<15000;i++) temp[i]=0;
    int pre=0,index=0;
    reverse(num1,n1);
    reverse(num2,n2);
    int n=max(n1,n2);
    while(index < n ){
        int a=0,b=0;
        if(index<n1) a=num1[index]-'0';
        if(index<n2) b=num2[index]-'0';
        temp[index++]=(a+b+pre)%10+'0';    
        pre=(a+b+pre)/10;      
    }
    if(pre==1) temp[n]=1+'0';
    reverse(temp,strlen(temp));
    return temp;
}